One thickness is perfectly fine. You can double if you want, but you don't have to.

Whether or not you have chewers... you'll only know by trying the hammock out. I've had ruthless chewers in the past, to the point that I couldn't use fabric in the cage at all. But right now I have guys who are more interested in PAPER... they're fine with fabric, but I have to keep tissues FAR out of their reach! LOL!