Did folding it cause any damage eg leave a crease or a white fold mark that plastic gets if stressed?
No. They are pretty thin and flexible.
I was worried when I took it out of the box, but after I unpacked it and looked it over I was surprised by how thin and plyable they are. I just straightened it and then bolted it to the car for a test fit. I left it there for a while and now it's sitting on the shelf waiting for me to paint the damn car.
Basically their only purpose is to redirect air - so they are not structural or thick or anything else of the type.
Just imagine a ice cream container lid, except long and black with a little bit of shape... Thats about the best description I can think of at the moment.
ONE WORD OF ADVICE:
Spend a couple of bucks and buy the mount kit while you're at it. It'll save you stuffing around and trying to find bolts etc. The mount kit is black so it'll blend in.
http://willcoxcorvette.com/advanced_search_result.php?cPath=1745&keywords=air%20dam