I have replied to a post like this before. DO NOT CAULK. I was warned very sternly by my Jayco Service dept when I took delivery of my Jayco 213.
Water cannot get behind the tub surround. The reason it is not caulked is because the tub and walls flex while the trailer is being towed. The caulking would crack in no time. The tub has a lip that goes up an inch or two behind the surround, so there is no way that water is going up there.
2010 Jayco JayFeather 213 EXP
2016 Ford F-150, 4x4, 3.5L ECOBOOST, MaxTow, Supercrew, 6.5FT, 3.55 axle