Found something interesting at Harbor Freight...
 

Found this today, Harbor Freight Tools - Quality Tools at the Lowest Prices

Thought it might come in handy for mods. Could be used for deflectors, spoilers, air dams, etc. It's tough rubber so would last. There might be other places to get it as well but this is probably the least expensive.

the harbor freight one kind of sucks; fairly floppy Ok for garage door not so much if it has to stand up on its own
A buddy bought some from a local garage door supply and it is very very tough. (he used it for a garage door)