The Dicor caulking I have used to repair the roof would work in the shower. However, a good quality latex bath and shower cauld will work just as well only cheaper. The shower surrounds are probably an ABS plastic glued to the walls.
Jeff and Deidra
1999 Jayco Eagle 283G Motorhome
2015 Ford F350 Lariat Ultimate
2014 Heartland Cyclone 3110 Toyhauler
Baton Rouge, Louisiana