Welcome to the forum. Your leak could be as simple as the trap fittings need tightening or you could have a cracked trap as I did. Of course your coach is a lot different that mine, but if it was made by Thor,.......................
A suggestion would be if you can see it with a light, run some water in the shower and see if the leak revels itself.
I'm sure others here may have some info.
Good luck and happy trails.