2017 Tundra Hidden 5th Wheel Rails / Under-bed installation

Alright so I had been searching forums for a long time looking for feedback on installing a hidden 5th wheel rails similar to the F250/350s factory setup on a Tundra 5.5ft box and couldn’t find anything. It seems everyone is installing the generic 5th wheel rails that are visible in the box and not ideal... fortunately their is a better way. If this was already done I apologize, and before i start i am within the tongue weight and tow rating for my truck, I'm not interested in debating if a Tundra should tow a 5th wheel or debating the setup or weight. I'm also not taking any responsibility for the modification or a certified mechanic in any way, i am an average backyard mechanic capable of most repairs. The install will work and fit, i have 2 years on it currently without any concerns and it looks clean. I commented below as well but when you compare what you are drilling, mounting and the brackets used on the install with a generic 5th wheel rail kit that sits in the box, this Reese under bed kit is obviously better built and stronger, the generic rail kit still needs drilling.

My Truck is a 2017 Tundra CrewMax 4x4 5.5ft box
my trailer is a 27ft and has rounded corners and designed for 1/2 ton short boxes.


What you need
- the 2019 F350 Reese under bed 5th wheel rails will fit (Reese Elite 30126) i picked it up off Amazon for $600
- you will also need a hitch designed to fit the rail kit, their are a few options but i picked up a nice used Reese 25k hitch
- You will need longer bolts and hardware i didn't measure the sizes but plan a trip to the hardware store if you don't keep a stock in the garage
- hand drill and a decent set of over size drill bits
- a friend to help or 2
- a way to lift the box off of the truck
- a grinder / cut off disks if you want it too look nice
- level, long square, measuring tape, markers
- a center punch
- About 6-8hrs for average skill level familiar with taking a truck box off, be prepared to be without your truck if you need to run and get something for a day or two, we broke a drill bit but i had a spare.
- torx set and wrenches
- a shim set sized for the hardware bolt size, 1/32,1/16..etc
- no welding required
- a decent metal hole saw kit

Now that you have all that lets get to the fun stuff
- Start off by going under the box remove all the clips for the lights, and trailer controller at the back close to the bumper, their are 4-5 to do. I believe you have to remove the tail lights to get at a couple but its been a while
- the hose connected to the gas tank has to come off
- now all you need is to remove the torx bolts you can see in the box
- before you take the box off, take a look at where the rails will fit, its very tight but the center of the rails should sit about 1" behind the axle center. I actually marked with a white marker on the frame where i had room to fit the rails between the frame and the box without hitting anything
- at this point you need to remove the box, i attached a photo of the box off but didn't really plan on doing a write-up on this one until my wife said i should for anyone considering this
- Once you have the box off you will need to do some fit up of the Reese under-bed rails, no holes lineup but it will fit
- assemble the rails and put them on the frame to figure out where it goes, for reference it will sit about 1" towards the back of the center of the axle
- once you have it visually where it should go make sure your center side to side and have it as close to center of the axle as possible
- put the shims under the Reese kit and level it true to the frame and then use the holes on the hidden rails and mark them on the frame where you need to drill.
- the Reese kit will bolt through on the top of the frame and not need new holes on the Reese kit only the frame but also you need to attach the side brackets to the side of the frame and drill holes. For the side brackets (angle brackets) you will need to drill new holes in the Reese kit as the F350 frame is wider.
- I cant stress the next part enough, take the rail kit off, now using your tape measure and square make sure all your holes are square and true. If you don't understand this part check out how to frame a wall building a house or squaring anything, you need to run your tape diagonal, and cross to ensure your holes on both sides are 100% parallel and perpendicular and straight to the frame. Take your time, its not difficult but you need to be diligent, your square will help.
- once you have done that and if it wasn't matching put your frame kit back on, recheck, and repeat the last couple steps until you are satisfied.
- at this point your ready to drill, before you do you want to be 100% sure the box will fit, if you marked like me on the frame you should be confident, if your really concerned test fit the box. Its fairly obvious that it will fit if you checked before you took the box off and are paying attention, i didn't need to test fit the box back on but i did have a look before i drilled.
- Now lets drill some holes , use your center punch and center punch all your holes, drill them out and note my next comments for sizing
- I copied the factory Reese install manual at this point, whatever bolts size and grade they provided i used with a longer one if needed, i also drilled the holes the same size as the factory kit would use on the F350.
- Now once you have drilled everything test fit the frame and hand tighten the bolts dont forget to shim it level, if you missed or one is out, i suggest you rework the 5th wheel rails as needed and not drill anymore or weld on the frame but it really should fit if you took your time
- you will notice the frame rails overhang the frame side to side, its not required but i did go ahead and cut the overhang off, i marked it with marker , removed the frame rails and cut it off.
- At this point torque everything down, again the Reese manual will give you the torque specs for everything. Don't overthink this part, your installing a 25K hitch kit on a truck rated for 10K, the bolts, and torques will be fine, if you want to tow 25K good luck to you. If you have ever installed the generic rails or look at them you will see this setup is far superior in terms of strength and drilling into the frame, hopefully that puts you at ease if your concerned.
- with the frame rails installed you don't want to put the receive cups (pucks) on it yet, to clarify they are the ones that the 5th wheel hitch connects into.
- now go ahead and put the truck box back on and bolt it down and connect all the wiring.
- the last step is to cutout your holes on the box for the receivers
- using a long drill bit or center punch climb under the box, you can see where the receiver cups (pucks) should be installed, there is a hole in Reese rails in the center for the bolt to hold it, using that hole as a guide mark and center punch the box from the bottom. its a little tricky from underneath so try and get it as close as possible, dont stress too much i have a fix if your off.
- now drill the pilot hole from the bottom with a small drill bit for all 4 receive cups (pucks)
- you can go to the top of the box and take a look at your holes, see how close you are to being on center for where the receiver cups will go.
- Use your hole saw kit, if you are off center a bit go a little bigger, the Reese kit tells you what size to cutout for them, go ahead and cut it out.
- now once its done test fit your receive cups, if they don't fit cut and grind, once it fits go ahead and bolt it down.
- the Reese kit comes with some cheap plastic covers to transition from the cutout to the receiver cups, I personally thought it was junk and didn't use it. If you want grab some PL glue or something similar that will bond to metal. Seal it all around the edge, use a spade or spatula to make it look nice and pretty and let it dry. I painted it black afterwards to match the box
- that's it your done, you can test fit the Reese hitch but you should be good to go
- I'm towing no more then the rated weight for the truck, and have a decent amount of KM on it since this mod without any concerns. I did go and re-torque the bolts which had not moved after a year.
- I attached a photo of the finished product, i also had a backhoe to lift off the box which helped.

 

Looks clean. How much does the hidden. Rails and hitch weight ?

 

The rails themselves are pretty light, i could not tell you exactly but 1 person could pickup and put them on pretty easy, the hitch is like any hitch you use on rails nothing special, on a good day i can lift it into the truck it might be 150 -200lbs. It weights the same as my old hitch that i used on normal rails, i added a couple more pics so you can see what the box looks like empty.

 

Man that is still heavy my dad has a 5ther I could use but the king pin is 750 that would put me over payload. I have been looking at turn over balls to try and do goose neck attachment.

 

https://www.etrailer.com/g-2019_Toyota_Tundra.htm?Style=6-1/2+Foot+Bed

 

I got one of those Anderson hitches for my 5th. It weighs about 40 lbs, using it with typical rails, I don't don't have the hidden hitch.

 

I have been looking at those

I have been looking at those

 

If you want to just have a gooseneck the modification is easier their is a plate that crosses the frame and is hidden under the box. It will work and I found someone that did it