Cleaned the 30G and 20G today with vinegar and water. Taped the tank for baffle attachment. Learned a few things.
1. Just because the bottle says 'Silicone I' doesn't mean it's clear. Protip: When it's labelled 'white', it is indeed white.
2. Mask off the baffle, too.
3. Wear a breather - fumes are nasty.
4. Dry-fit everything first. Obvious, but easy to overlook.
5. Use a little bit of silicon to start, then add extra once things are in place.
So instead of a 1.5" lower opening, I now have a 3/4" lower opening because I assumed I had dry-fit it already. I probably had, but then that was before the measurements were finalized.
I also got silicon all over the baffle panel itself. All that aside, it should turn out functional - and that's all that matters for this first try. In an hour or two I'll do the secondary baffle panel.