OK so I decided to learn how to make a proper base of this. I like those stackable display cases you see at Hobby Lobby, so I got one. Eric Rains talked me into getting some Clay-Shay. I mixed it up and plastered it on in one small sections, and pressed the M51 into it to create track marks. The super-easy to work with Clay-Shay, along with some pebbles and dirt from my neighbor's driveway, plus some pigments sprinkled when dry, came out looking like this:
I then used some Model Master Sand color and lightly hit it with the Sotar 20/20
After that, I got some of the old reliable Tamiya Flat Black and a few index cards to prevent over-spray, and got the remainder of the base
Then I put the M51 on...only to find that it no longer fit! I fought with it a bit, only to damage the track...AGGGGGHHH!!!!!!!!! So I took a bit to calm down, then glued it to the base as best she'd fit, then mixed up a tiny bit of Clay-Shay, and working it under the spaces, along with some or that leftover sand and pebbles from earlier, and worked it up under there. May need some dry-brushing once fully cured, but I think it came out looking pretty good!