Personally I've never had much luck with using metal foils, I just couldn't get convincing creases in it.
I did come up with a solution though, using the beige low tack tape painters use! Because it has one sticky side its easy to attach it in place on whatever you want to tarp over, attach sections to each other to create as in real life or to fold over the sides to make the double edge a lot of tarps have. Because it is less stiff than metal is can easily be shaped, but it's a bit stiffer (and more resistant!!) than paper napkins. You can also make realistic tears and damage in it!
To shape it (in my case a sd/kfz 251 cover) I cut down several sections like the real thing, stuck them together, put it on the model and then folded down the sides. After that I wetted the surface of the tape with Vallejo's Matt Medium (the big bottle that smells like apples, you can find it in art supply stores). After it soaked into the tape a bit I could easily form/drape it realistically with the brush. When dry it is still very flexible and you can coat it again to make some changes. On the last coat I let it dry a bit first and then went over it crosswise with the brush to get a scale 'woven' texture on it to simulate canvas.
After that I finished the rest of the model and primed it with Vallejo's black PU primer and painted it normally, with wet washes etc and it held up perfectly.
If you want I can make some pictures of the finihed results or a small step by step. Hope this helps!
edit; This is the tape I mean. A huge roll will cost you less then €/$ 1,- The cheaper the better because the cheap stuff soaks better.
