Project Finding "Nory" (Dory + Nemo) build/custom

Perhaps if you covered the bottom of the inside of the coach with something. Maybe 3d printing something would work? Or, if it fits, some kind of small cardboard-or-something pieces to tape together into a sort of arch for the wheels that can be fit to the inside, and it would keep any rocks or sand (maybe not sand actually) for hitting the wheels and axles. you could paint them blue like water or to match whatever else is going to be in the coach other than the figurines.