Everybody I've seen anchors out. When we were at the "Belize Yacht Club" two years ago, we inquired about slips and slip fees for our boat (40ft) - which was not with us. The answers we're very discouraging both in terms of availability and price. It may have changed, but anchoring safely behind the reef looks just great to us. (We usually anchor out anyway.)
I would check very carefully into the BYC situation before trying to avail myself of their services.