We replaced our water bladder last year with a plastic tank. The bladder was installed by the PO to add capacity and bring the boat back in trim; it was installed rather than a solid tank to allow access to other items like the hot water heater.
We found that the bladder leaked at the filler hose seal, even after replacing the tank, so took it out and installed a solid tank.
Meaning that we had to then completely rearrange the hot water tank, water pump, and holding tank to accommodate the new water tank.
Our new tank is rotomolded, which is the strongest and most inexpensive approach we found. Welded plastic tanks tend to be thicker, can leak more easily, and are very expensive.
The new tank, by the way, complements and balances (trim wise) our original aluminium tank.
Campbell River BC