To get some added traction for the treads, you could add some 1x1 studs
. I went to a Lego store and got around 500 green 1x1 studs at the Pick-A-Brick wall. Then, I spent half an hour sticking little studs onto the tank tracks. It makes it noisier, and the studs will fall off at times, but it turns better and has a lot better grip that way. Just make sure to go over the tracks every once in a while and make sure that all the studs are well secured.
It appears as if you can get them for one US cent apiece on Bricklink, which means you could outfit most tanks with two or three dollars, plus shipping, if there is no minimum order for the store you buy from.
-EDIT- Fixed some grammer stuff. Hiking is always tiring... and then my brain doesn't work...