I have a 30' toyhauler (bumper pull) that also had fresh water tank issues.
1) From the factory the straps holding it up were not equally spaced so the tank would bulge pretty badly where there was a larger gap between straps. I ended up buying some square metal tubing from a home improvement store and bolting it to the frame to more fully support the tank.
2) After several trips I was filling up the fresh water tank at home and had one end of one of the straps break loose - they held up the factory straps with self tapping screws and this one was put too close to the edge of the frame metal and just broke out. I replaced the self tapping screw with a bolt and nut.
It has now been holding up fine for 2 years.