Thanks Landy, for the analysis. Maybe I should switch back to cheap flooded.
I'm not concerned about mixing chassis and house batteries, and I don't need to start in cold weather because I hate cold weather. But I killed several flooded batteries, one because my pre-RV vehicles were old and didn't have parasitic loads, so it wasn't a thing I knew existed. And one because a light switch failed when the van was in storage. I did think an AGM would cope better with these deep discharges, as well as being slower to self-discharge in storage.
I also have memory problems, and can never frickin' remember that a full charge is a different voltage on an AGM. But I could solve that with a bright sticker.