Post a picture of a scratch built car. I will start with my track cleaning car, modeled on the Centerline car. It is made from wood with aluminum flashing epoxied in to line the roller brush pit. It uses Mini paint rollers with a 2 in long, 1/2 inch pipe coupling for weight. I use rubbing alcohol for cleaning fluid and it works very well.
Lets us see your scratch built car picture.
Charlie