Caulking top of shower

[Zapper]

Preparing to leave for a month in Fort Morgan, AL, in our new Fuzion. Doing checks and rechecks on different on parts and pieces, just trying to learn the camper.
My question: today I noticed the top of the shower insert, where it meets the wallboard isn't caulked. I don't see how water cannot eventually get up there. I'm going to caulk, although it won't be easy because of the depth of the insert itself, especially in the corners. Is this normally a caulked area? Has anyone else noticed this, or is there a reason to not caulk that I'm missing?