http://www.youtube.com/watch?v=2colMsliCqw Double-tracked is my attempt at a robust tank using the rubber treads. I used the rubber treads instead of the hard plastic treads since they have much better grip (and I have no plastic treads). This worked very well. The only down side to this is that there was no suspension. Also, the gears connecting the front and back treads would often catch on the ground. Overall though, I think this could outperform almost any other Lego tank the same size with hard plastic treads.
Instructions can be downloaded here(Pdf).
3D files can be downloaded here (Zip).
Check if you have all he parts by going to rebrickable.