leaking shower valve

[2Stepn]

I found water leaking into the shower and also leaking out the exterior corner of the trailer under the shower. Since I was camping, I removed the shower valve and found the threaded connections on the back of the shower valve to be loose. I tightened them and that solved the leaking problem, but I found that when I went to reinstall the shower valve the pex and related fittings are too long and won't properly fit into the opening due to hitting the wall behind the shower enclosure without forcing them into place.
I think this is forcing the lines to be twisted, and do to vibrations while going down the road is the connections loosen and start leaking.
I took the trailer to the dealer to be repaired. They retightened the fittings, forced things in place, and I was told They are ALL that way.
Guess what, it's leaking again, Looking for ideas on how to properly repair this problem, the dealer is no help!!!

 

[danemayer]

PEX is pretty easy to work with. I'd suggest picking up some Sharkbite (or equivalent) push on fittings like these at either a hardware store or plumbing supply. A cutter like this will help you make straight cuts. Cut out the extra tubing so it fits better. Just be careful to not cut out too much or you'll need more fittings and some extra PEX tubing. It would probably be a good idea to also get a removal tool in case you need to take the press-on fittings off. Total cost and time will be far less than taking the rig to the dealer and back.