For starters check out and consider joining the RMHYC. They have negotiated some nice discounts with most marinas especially if the boat is going to be there long term.

As a marina suggestion Boat Harbor at the Abaco Beach Resort. I used it as a base a couple years ago and found it secure and fairly well protected. As with all the Marsh Harbor marinas there is a fairly large group of people wintering over. It was about 2/3 power, 1/3 sail with everyone friendly and actually more like a community than a marina. Getting around town (groceries, hardware store, etc.) wasn't bad. We used our folding bikes pretty much all over the town.

Boat Harbor http://www.abacobeachresort.com/marina.html

Marina list http://www.go-abacos.com/cruise/ab_marinas.html

RMHYC http://www.rmhyc.com/content.aspx?page_id=0&club_id=481507