Do it
I think a flex type bladder of +-15 to 20+ gallons would work well under the v- berth. They normally require strong attchment points, easy in this area. The fill line is the issue. Never have done it, but I see two or three choices. 1)Hose would have to come up behind the curtins and through the deck. (ugly). 2) Hose would have to be painfully routed into the bow and up into the anchor locker (a lot of foam scraping) 3) Route a fill hose from the bladder around under the seats, under the galley, then down under the rear berth sole and out into the space near the battery, then up and out through the aft to a good fill location. (draw back, always will have water trapped in the fill line due to the routing elevation.) My 2 cents worth, sounds like I should give it a try, we have a 12 gallon blatter under the galley sink with presurized water to both sinks and a aft shower.. I would like to move it forward and increrase the size!Steve