I had flexi tanks on a previous boat, not a Bavaria, where they replaced the original galvanised iron tanks that had been fitted when it was built in the mid 60s. A previous owner had fitted them and they were easy to take out and refit. Just make sure before buying and placing one into the storage area under the forward cabin berth, that when full of water the resulting change of trim causing the bow to be lower in the water than before, does not adversely affect the way the boat handles. Personally I would be more inclined to use the bilge area under the floorboards within the main cabin, where this would have an almost neutral affect on trim. In this situation you would probably need to fit extra screws to hold the floorboards down where the flexi tank would expand upwards, as well as in all other directions, when full. On the previous boat the water tanks were located port and starboard, and had individual filler pipes. For drawing water out of the two tanks, the draw off lines were fitted with non return valves allowing water out, but not back in, and with both tanks being emptied together. This to a large extent ensured that water would not run across to the low side when the boat was heeled but as indicated! the system as fitted, was not 100% reliable. The alternative would be to fit proper shut off valves which would allow each side to be used as needed, but the system worked well enough as it was.
