Looks great Adam.
Puts my old girl to shame.
Probably too late now, but under the bottom rack would have been a good spot.
Maybe grab 4 pieces of conduit and put it vertical up the side of the bottom middle rack. Should still leave enough room for a smaller board and you will have the length for a big mast in the middle there.
I would get another piece welded in to hold the conduit in place. I screwed some conduit in to hold my extensions but they vibrate loose after a while.
Jeff's has pretty good set up for masts on the edges I think. I was going to do that with mine, but I picked up an old sail bag with the slots in the bottom that fits nicely in the bottom sail rack.
Keep the photos coming.