MOWINGMAN. Rocks work! Lol.
Years ago I had these O scale light as a feather older issue Atlas boxcars that I would epoxy to the not visible inside floor stacks of pennies. Then I made things easier with automobile tire weights. Easy with the sticky tape on one side a roll of them set up side by side interior. These were especially well suited to Weaver PS1 covered hopper cars of which I used to switch on my O scale modules. They wouldn't fall off narrow curves!