Richard, a word of advice concerning the rear hatch. Try and find a way of ensuring water does not enter the hull via the hatch on the rear deck. When I built my Sentinel, I was somewhat inexperienced in such matters, and have since found that water can get into the hull via this opening. Sentinel has a respectable turn of speed, and if you stop quickly, the stern wash can come over the transom onto the rear deck, and into the hull. Had I known it at the time, I think I would have attempted to devise a way of making an internal coaming to try and prevent this happening. It would be much easier to do this while it's still under construction. I have not tried a retro fit, as it were, instead I reduce speed gradually to prevent water coming over the stern.
Peter.