Topper to truck seal around back window

I have a First Gen double cab with the roll down rear window. I recently picked up a snugtop topper with the flip up front window.
The roll down rear window is one of my favorite things about the truck so I'd like to keep the topper window open as much as possible. Is there a way to seal between the windows that works well?

I've seen seals & I've also heard of inflating a bike inner tube. Figured I'd post to ask the knowlegable crowd... Search didn't find anything.

 

https://www.custompickup.com/shop/index.php?l=product_list&c=18

 

Use pipe insulation. I've tried boots and they just dont really work well since the topper opening is smaller than the rear window so shoving pipe insulation in between the cab and the topper is about as good as I have found so far, it wont be water tight but its pretty air tight.