Let us know how this project progresses, I've entertained the idea of making a predator costume in the past, but had no idea where to begin. I too would need a bodysuit, or I would be one tattooed predator.
I think the only problem with the cotton would be that it wouldnt have the sort of glistening-slime-like texture the predator has. Latex would be the best material as far as texture is concerned, but I have no idea how easy it would be to paint a latex body suit. I had a friend who designed fetish "clothing" and had made many full-body latex suits. I havent seen the guy in a long time, but if I get ahold of him, I'll ask how difficult and expensive making and painting a latex suit like this would be.