Take a look at this stuff I found at home depot as we remodel our Boler
1/16 in. x 4 ft. x 8 ft. Plastic Panel-63003 - The Home Depot
We were going to go with a rubber type roll insulation or the silver "bubble wrap" stuff and go over that with foam backed auto headliner...then we found the stuff above....
It is extremely flexible and water proof, and is not brittle...and they have molding for the seams in between pieces and round edges...very inexpensive stuff too...seems like it would be very durable and easy to clean...
If you should go with auto headliner don't buy at an auto parts store...go to a fabric store it is much cheaper and they have a better selection...we found a huge assortment of colors at Hancock Fabrics Foam Backed Automotive Headliner Fabric - Desert - Headliner Fabric
and a roll 60" wide was about $15 a linear yard and you can get coupons for it for up to half off!
I like the headliner just fine but I don't think it will stay clean with a 2 year old boy camping in the woods so we thought the plastic panel sheets would work better & easier to keep clean, we are even going to use it to line our shower walls on the boler
... I have another post on my rebuild here if you want to look:
Our 1971 13' Boler mods