http://www.mcmaster.com/nav/enter.as...2&pagenum=3258
Push-On Edge-Trim Rubber Seal Bulb Next To Grabber, 1/32" Edge, 3/8" Bulb Width
That's the stuff I prefer...was 95 cents per foot last time I ordered it, and it works great. I like that it's a "bulb" seal rather than a solid foam pad. That way it can grow and shrink as needed as the canopy contracts in cold and expands in heat. And it doesn't apply any force against the canopy & side deck. The bulb compresses and it just rides there, filling the gap. The bulb is 3/8" but can compress way down without force. Good luck using 3/8" foam...it would be too fat.
I used a foam seal once and my canopy got stuck latched because of the decompression force of the seal.