Moderators might want to move this, since you're in the classified ads section, not the photography section.
In terms of the rig, I can tell you what I do.
First, under those conditions there's somebody on the boat. Either I'm a tourist and it's a guided dive or I'm working and I'll make sure I've got a boat tender on board.
Second, I just hand the camera up to somebody on deck.
Now if it's calm day and I'm not worried about it, I just clip the rig off on my BCD or else (with smaller boats, like inflatables) just put the rig up and over the side myself.
Not done this myself, but now you've got me thinking. You could rig a line over the side to tie it off on while you board, then haul it in.