I installed the large cap next to the inverter first. That wasn't enough, but the only fault then was OOL, meaning the inverter stayed in overload too long. After installing the boost-start cap on the a/c, the inverter chirps twice for a total of about a second, but the compressor spins up immediately and everything stays up.
The van's alternator has a hard time at idle in gear, but that's not suprising.