wing_zealot wrote:
Mine's caulked. And why would there be moisture behind there in the first place unless you have a leak? And why would you need such a big gap? You expecting to drain a torrent of water?
Google "RV tub gap" and you will find tons of threads on this. I suspect someone other than the factory caulked your tub if it's not the overlapping design. I guess the theory is condensation trapped behind the wall will promote mold growth and the air gap allow that moisture a place to vent.
I have found threads discussing the same thing in home shower installs where some builders will not caulk small areas for weeping.