Having just done a repair to the P-trap under the tub, I noticed in my labours that there was a lot of flex around the drain as I was trying to get the trap disconnected and the drain removed (another tale!).
Fortunately I didn't crack anything, and I have the P-trap repair finished.
Not having used the tub yet (new-to-me trailer last summer, haven't used the shower yet, and still working on it) I wasn't even aware of it. Glad to have found this thread (wish I had found it BEFORE I had finished the work on the P-trap repair
). Going to have a look under there while I have the trap cover off and see if I can address the problem from underneath without removing everything I have just put in. If not, I will just be very judicious when I use the shower, and avoid the front end until I can get the outdoor shower pulled - have to do that anyway at some point - couldn't get the old, stiff shower hose back into it's cubby when it came time to winterize and then close up. So I had to cut it off in order to close the door.
Followup…. Went back and checked. My tub is actually pretty solid. Right over the drain is a little soft, but not overly so. So looks like I lucked out there.