I did one so far (for an M4A3 75w), but three more to do on in-progress Shermans, and I just used copy paper that has a slightly glossy sheen to it. I just painted it, measured out the lines, cut it out, painted the border, wrinkled it a bit, added it atop the stowage, and then roped it all down with wood model ship rope. Worked okay.
Oil cans often on the right front fender, especially on 6th Armored Div tanks. But you could also sometimes find them mixed in with the stowage on the back. Mostly, the back stowage tends to be various bedrolls/bags/crates/ID panels, with the occasional odd civilian item thrown in.
Look forward to seeing it complete.
Rob
P.S. If this link works, you can see the one I've done. This was a dio (my first) I did about 6 months ago, trying to use all things I had around (didn't want to buy anything new). If I had it to do over again, I'd have done the cobblestones more different colors, more rubble, etc. But I had to declare it done and move on. I made all the bricks and cobblestones myself.
http://new.photos.yahoo.com/biggsgalassi/album/576460762314299187