Can't speak specifically to the Moorings, but we always elect to spend the night onboard our TMM charter boat. While it costs 50% of the daily boat rental, it provides lodging for 4 couples. I think it's got to be cheaper than staying elsewhere.

In addition, everyone gets situated in their staterooms, and the crew gets familiar with the boat over the course of the evening. And if you have your provisions delivered, you have the opportunity to get them all stored and organized that evening as well. Come morning, get your charter briefing done and you're ready to set sail. And now that we always choose a boat with A/C, the nights are cool and comfortable in the cabins. I think staying onboard the night before has a lot of advantages.