Here's a home-made track cleaning car I built out of some wood scraps and spare trucks. The main body is 1/2" x 2-1/2" oak board. It holds a scrub sponge that I bought at the dollar store (comes two per package). No cutting required, just press the sponge in. The sponge can be used dry or else wet it down with some cleaner (admittedly, I haven't tried it wet, yet). I can also set a metal plate or small brick or similar on the car if I need to weight it down a little more.
I really haven't fully tested it that well yet, since my layout isn't THAT big and can be hand-cleaned about as fast as getting this car out and ready to go. But it might have some potential. It could probably snag on something here or there, but perhaps whatever it manages to snag on needs filed down a little bit anyway.
