I have the bigger brother 37.5
and had to replace the wooden cleat behind and above the big rear aft cabin access cover because it was a little rotten. I am referring to the removable plywood panel which is held in place with three slide latches. The cleat I am talking about supports the shelf in the first set of compartments with the big covers which hinge toward the center of the boat. The bulkhead and shelf are still solid but would have rotted too if I had not replaced the cleat.Can you tell me where your boat was leaking? I have reseated the cockpit ports and sealed all of the screw holes under the quadrant cover with epoxy. I cannot tell any other place where water is coming in but it weeps slowly out of the upper center bulge in my aft cabin head liner which is just under the pedestal. After a rain, it drips for days. I cannot figure out where it is coming in or where it accumulates. I am assuming that it wicks out from the headliner somehow.I do not know about your fuel tank but I just replaced my holding tank with a 28 gallon polyethylene one made by Moeller. It is 15.5 inches high, 23.5 inches deep, and 20 inches wide. I had to put it in with the fittings to the rear and cut out the bulkhead to the very aft compartment to hook it up. I also had to build a platform and bracing for it but it fits - barely.The teak trim which holds the big access cover had to come off to get that tank in. You might need to do the same. Just gently pry the top trim piece down in the middle and cut it with a thin kerf Japanese trim saw. Then you can pry out all of the trim one piece at a time. This trim is stapled into the bulkhead so you may have fixed that somehow yourself by now. I am interested in more of the details of the bulkhead replacement you just did. Do you not have an access cover now? Is that why you need to put the tank in from the top?Does your boat have two sets of lazarettes like my 37.5? A few more details would help us understand your situation.