My boat has the same setup as yours; most loads on one 30A side, and the HVAC
(and a few other loads) on another 30A side.
I use a 30A splitter to two 30A cords. My home dock
has two 30A outlets, but I only use one, mostly because I'm too lazy to string two cords along the deck
, and also to keep my other 30A cord out of the sun & weather
I have a 50-to-30 splitter I can use if 50A is available, but I don't find the need to pay extra for 50A service
at a marina. I can run two air conditioners at around 10 Amps each, and still use other appliances
, staying well within the 30A limit.
During this past heat wave, I did have to forego running the electric water heater
with the air conditioners working full-time, but that wasn't really much of an issue.