That's the way I have mine installed and its worked fine for several years - I did level the pit when I put it in by shimming around the edges.
Nothing wrong with that option at all. I did it for my first layout and had no problems. The only consideration is to allow access to any mechanism below the pit. So, you'll want a substantial hole, say 6-8" in diameter. The pit, itself, must sit in a custom-cut hole, but the lip of the pit is sufficient to hold it all up and in place, including with an engine on it. In my case it was only 1" foam, although that layer was atop 5/8" ply. Other than that, I merely set mine in place, careful to have it sit flat and flush with the foam all around the circumference, and I didn't even need to use any tacky substance. Placed, wired up, and played.
-Crandell
Does anyone have any pros / cons, tips or tricks for installing the walthers 90ft turntable into the 2" foam base over open box consruction?
Thanks, Stratfan12