Thanks for the info... I thought the install costs and such would be significantly more, so this is great news! With regards to AC units, we think we can get away with a single 16k BTU unit connected to the same vent system our Webasto is connected to. The 5k-6k units are what we think we can fit in the space beneath our cockpit.
My 41" foot steel cutter pilothouse thingie has a 12,000 BTU Mermaid Marine Air unit that is perfectly serviceable, also provides heat, and that can (barely) be kicked into life by my Honda 2000 luggable genset. It's the 15-20 amp initial start-up draw that demands the big generator, not necessarily the "ongoing cooling".
As it is, I've decided to only use the A/C at dock. I have just enough inverter output to run it off batteries, but come on...they'd be dead in three hours!
Interestingly, I am considering a Webasto or an Espar, but I'll have to redo the conduit that already hooks up the A/C, because the heat from the MM Air unit is not nearly as hot as the diesel burner output, which I think would melt the existing conduit.