If they're temporary, just print them out of plastic. the MTH cars are not that heavy, and the print will be the weakest in the Z direction, so just print them flat on the mat. I suspect they'll be just fine as they're thick enough to have a decent number of layers. Larger layer height is stronger than smaller ones, and the fidelity of these doesnt matter... the layer lines arent going to matter. Try a .6 nozzle and let em rip. I doubt they'll snap. If anything, they might flex or stretch a little.
If you print them yourself and they break, what are you out? $.50 worth of filament? Absolutely worth a shot to see if it works.