Better to have holes poked into the build now than next week! Please continue to do so! :P
So I did a mini-test, filled it with about two inches of water for five minutes. No leaks, didn't instantly shatter. Looked at the seals, and no water got underneath them. I think it'll be okay, so long as I'm very, very diligent about emptying the false bottom, via the PVC method. Looking around the internet, others who put far more water in it than I'm planning on (up to half a tank) say they've had no issues. Of course, others say it's cracked on them, so.
I think this will work.
So, the plan is, make a 2-inch egg-crate false bottom, and an egg crate, like, divider, to hold back the substrate when I remove the water tub for changes, with a PVC pipe for drain access. Then three-or-so inches of Eco Earth x ABG. Load with springtails and another plant or two, and call it golden.
Uh, and then Fire Belly Toads.