The piece fits perfectly - I'm liking the look of it already. After waiting a half-hour for the silicone to set a bit, I'm ready to start foaming. I'll be using Great Stuff Pond & Stone Insulating Foam for this part. It's important to find foam without unsafe additives, and since this stuff is safe for fish, it's safe for geckos.
It's also messy.
And it's here that I make my first rookie mistake. Vastly underestimating how much foam it would take to fill in the background, I only purchased one can. You can see the progress I made off of just that one.
Not very much at all.
Welp, I guess I knew there would be setbacks. I've gone ahead and ordered two more cans of Great Stuff on Amazon, and since I'm cheap, I'm using standard shipping. So... guess the project is on hiatus until I get more foam. There are some things that still need to be finalized (substrate, drainage layer, plants), so I'll work on getting all that situated in the mean time. I'll update next week once the foam arrives and I have a chance to continue.