Insulation between topper and cab

Has anyone set up a good insulation system for the gap between the topper and and the cab? I would love to be able to open the window, run the car for a few minutes and heat up the topper for camping back there.

Most things I've thought of would be pretty hard on the paint of the cab (don't care about the paint on the topper so much). If anyone has any ideas or things that have worked for them, let me know!

 

Everything you need can be found here...

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

Even has a way to protect the paint on your can at bottom of page

(found with simple google search)

 

May sound too simple, but I used a heavy duty bicycle inner tube. Put it in place, inflate a little, adjust, inflate more. Worked very well. A light coat of silicone spray made sure it didn't rub paint. Kept water/snow out pretty good.