Hey Casey, after talking to you at Fisk's, I remembered something.... my neighbor has a trailer for spraying urethane, both the rubber type for linings, and the foam, for industrial jobs.... Whether he does it, or you find someone else who does, it could make for a HUGE amount of filler material all at once. I assume they have waste that they need to get rid of, whether for testing spray patterns, or for cleaning out the lines once a job is complete. Maybe one of these people can spray some foam, say on a 4x8 sheet of styrofoam, for you. Then, being he also does the polyurethane coating, maybe they can coat that foam for you also? Or, if you know the person well, maybe they'll just do it cheap to free.
And no, I'm not setting up a crawler coarse in my basement LOL! A dirt Mini-T track, maybe!