Aft Tank
I have a 2001/331 with the same problem. I opted to install a bladder tank underneath the aft berth instead of the lead. It wasn't very difficult. I have a vetus tank that holds about 30 gallons. I got a manifold from beneteau to plumb in the extra tank(s). I use it primarily for the balance of the boat. I liked the idea of having more water capacity so I installed a rigid tank from Beneteau under the starboard settee. I believe you can still get it on the Beneteau parts website. It takes several weeks to get it because it ships from France. The tank takes up nearly all the space under the settee, but it helps a lot with the port list. Not an easy job, but with the three tanks I have over 100 gallons of capacity. I use the starboard tank as my primary and only fill the front tank when I'm going to need it. The aft tank is the- hey we are out of water- emergency tank. With the starboard tank full, and the front tank more than halfway full, the bow will still sit too low in the water. The aft tank brings the transom right down to the waterline, but my boat sits better on its lines and the extra weight is useful rather than the lead bars.