Foam weather stripping

I'd check with McMaster-Carr, Grainger, MSC.

http://www.mcmaster.com/#standard-adhesive-backed-weatherstripping-foam/=qfrgec

Might check Log Cabin sellers. Ours came with rolls of sticky back foam to put between the log courses. Might work for you.

http://www.foamtapes.net/

watch the product they sell some with the foam and the sticky tape sold separate

Closed cell foam tape with sticky on one side?

Try your local truck cap dealer. They have stuff like this usually in 35 and 42 foot rolls for installing truck caps, rail type tonneau covers, etc. The rolls are usually enough to do a short bed or long bed twice. They usually carry different widths too.

Accessory Warehouse on Rt 12 in Groton (1/2 way between the 95 overpass and the main gate to the Sub Base) is where I got my last batch.