Thanks for all the feedback. I did double check and the specs for the 2016 Lagoon 400 on SailCaribe shows a 79 gal capacity. Even checked to see if it had a water maker but it doesn't show it in the equipment. In my experience though, 79 gal is REALLY small.

I think we're going to check with SC and hope they have 2 - 5 gal jerry cans and we'll try to fill them every time we go ashore. It is both an experienced and low maintenance crew so I'm sure we can both conserve and refill in increments as best we can.

The resort is tempting, on our last BVI trip we took 1 day on the dock at Scrub and really enjoyed the break. However I'm not sure it's worth the trip over to USVI. We'll run it by the crew though.

BTW, I was doing the same calcs as Sail2wind ... 30 gallons is HUGE and way too heavy to move around a dinghy and then haul on board. And filling the dinghy is clever but ... never gonna happen.

Thanks again for the feedback, if there are any suggestions beyond the obvious (bioluminescent bay etc) feel free to chime in.