The galvanized tank holder it supported by lag bolts secured to the subfloor. You clearly need to replace the subfloor.
I learned the hard way: you can’t get to the subfloor without taking the bath out – which can’t be done without taking the bath wall out – and removing the inside skin (to get to the c-channel that sandwiches the sub-floor to the out-riggers). And the inside skin starts up front past the gaucho and refrigerator … so you basically have to gut the entire Safari to replace the subfloor in the rear bath.
Before putting in the new subfloor, I added a piece of angle iron to the frame for the galvanized tank holder, so it would have something besides wood for support.
Related pictures are in my picture gallery.