Buy an exterior shower faucet axillary box
Decide on location...then cut an opening in side of RV
Frame the cut out opening for support and something to attach shower box to
Locate COLD water line....install a 'T' fitting and then run new cold water line to shower faucet opening
Locate HOT water line....install a 'T' fitting and then run new hot water line to shower faucet opening
Connect hot/cold lines to faucet connections
Install shower box into opening
'T' s , PEX line (1/2") and fittings any Home Depot, Lowes, ACE Hardware
Sharkbite, Gatorbite, FlairIt fitting are easy to install...just push on PEX line
They also have the PEX pipe