I found a light weight fold up baby stroller at a yard sale for $7.00!!
The wheels that came on it are perfect for this prototype. I’ve mounted them up and they fit great. The tire is made of high density closed cell foam so they should grip well enough.
Now it’s all about fabricating the drive mechanism. I might experiment with some gear reduced electric motors I have just to test the traction. Eventually, I want stepper motors on all six wheels, preferably built into the hub. We’ll see about that one… so far my searches haven’t turned up anything affordable. Electronics “salvage yards” will be the place I’ll end up finding what I want.