I did add an outside shower on my TT. The only place I felt comfortable adding it was where I had inside access to know I was not cutting an outside shower hole that would have been obstructed by who knows what. So, I was able to plan the cut and see inside where the shower module was going and both water lines passed right by the area making it very easy to cut the Pex and use the proper Pex T connections for the outside shower. I have never had a problem with any leaking on our outside shower or the connections I put in.
Just make sure that new outside shower is added to your winterizing routine, if you winterize.