I've got a bathtub in a 22-year old track home, and the bottom of the tub flexes whenever it has weight on it. I assume that this is because this is a low-end (tract home) fiberglass tub? Should I be concerned about the bottom of the tub cracking and leaking? Are there warning signs that I should be looking for? Or should I just go ahead and replace the tub?

Thanks for your advice!