Thanks, everyone, for the comments!
The middle divider in the bubble trap is 1.5 inches above the bottom (that's why it's taller than the other two). The baffle for the refugium may be too tall. I'll find out when I leak test.
The plumbing will have an return pump pipe with an offshoot pipe with a gate valve so that some of the return water (25% or so) will fall into the 'fuge and the rest will be sent back to the DT.
I made the return section larger because I used melev's design and he recommends a return section with enough water to keep the tank running for at least two days unattended, juuust in case.