Need some help asap

No dispute there, Bobbo. My thought was that a loose trap etc. connection is even MORE likely in RV than home. What with vibration and all. Sure we need to fix them. I hope there's an inspection hatch somewhere. I can't say that all that much attention was paid to detail on our coach, but there are accesses for both shower valve and shower drain.

j-d wrote:
Traps leak under residential sinks and vanities. Could easily leak in an RV.

Not when properly installed. If a trap is leaking either at home or in the RV, it needs to be fixed.

Shower pan cracked...

Could be both issues noted above. Like this: Shower's connection to piping leading to the gray tank is loose. All OK till gray tank is full. Then, some of the backup that would come all the way into the shower leaks out below it.
Is there a way to take a look below the shower? Ours has a little detachable panel that lets me see the shower trap. Traps leak under residential sinks and vanities. Could easily leak in an RV.

If the water is coming up the shower drain, its time to dump your grey tank. On the other hand, if the water is running out from under the shower, not coming up the shower drain, you have a leaking water line under the shower.

When my gray tank is too full, it backs up into the shower. Time to dump.

Gray tank backing. Because it is full?
Loose connection in shower water line.