"...breaker box in the closet wall be behind will be sharing the wall with the end of the shower. "

The panel is not allowed in a clothes closet, but backing up to a shower wall is acceptable.

thanks for the reply. it cant be in a closet even if it isnt the main breaker? the main breaker and first floor breaker box is outside, this is the breaker box for the second floor. im not to worried about code since this is an older house and i live in the middle of nowhere I just wanted to make sure that having it there wont cause any forseeable electrical problems or corrosion as long as i have a good vapor barrier up.

No panel box, sub or main, can be in a clothes closet. If it is a utility room with no room for storage within the 30x36 area in front of the panel then it is acceptable.

The panel may well have been within the current electrical code when it was installed in the closet. I think that used to be allowed. If it was, you don't have to move it just because you are working on the other side of the wall.

You definitely want to protect the breaker box (and just about any wall from shower moisture. If you're using a preformed shower stall, that's usually not a problem. If you're doing your own tile job, then you need a continuous moisture barrier behind most substrates (such as greenboard which I DO NOT recommend or the concrete board products) or use one of the impervious substrates like GP's Denshield (properly installed and siliconed joints).