I have a 1988 33.5. The original aluminum 52 gal water tank under the vberth started leaking shortly after we bought the boat in 2005. I tried unsuccessfully to patch the tank with epoxy.
I contacted Hunter and they gave me a procedure to remove the tank, the name/address/phone of the original tank manufacturer and also sent me a .jpg drawing of the tank. I really did not want to put in another metal tank so I contacted Ronco and sent them the drawing. They were able to make a poly tank.
Tank removal was a real PITA. I had to remove the vberth decking which involved cutting the tabbing along the hull, After the decking was loose, I had to cut the deck in half to get it out of the vberth. The old tank just barely fit through the vberth door. I had to remove the aluminum trim on the archway from the salon into the vanity area before the tank would pass through. I had to build and fiberglass in a new tank support platform as the old one was water damaged. With the new tank installed and plumbed, I used the old deck as a pattern and cut a new deck from marine plywood. To install the required tabbing, I had to peel up the carpeting on the hull, prep the hull and and epoxy in the roving tabs along each side of the vberth.
Good luck.