The interior needed to be sealed completely while building it, and now was the test. Sure enough, the first layer passed with flying colors. No leaks. During the first pour of several, I did encounter several bubbles that came up from the bottom of the flat books in the lower left.
I reached in with a sharp object and popped the ones I could, but worried about drying during the night: would they freeze in place and wreck the scene? There was no way to reach in from the top with the torch to de-gas except through the little hole in the top of the box.
The next day I checked. Looks like all the bubbles had risen to the surface and hung there! Fortunately the epoxy was still malleable, so I was able to reach in and smash them.
When that dries, the next layer can go on. Meanwhile, I started on the door. This is your basic, run-of-the-mill shop door, but they take time when layers are involved.