There is no caulking on the bottom for a reason. Our RV tech told us that it is due to the flexing of the trailer during travel, that the caulking would just crack and let go. The shower walls are designed with a lip, to prevent water from getting behind.
2010 Jayco JayFeather 213 EXP
2016 Ford F-150, 4x4, 3.5L ECOBOOST, MaxTow, Supercrew, 6.5FT, 3.55 axle