Determine the type of shower you will install. Standard RV showers are mounted flush with the exterior of the RV and have a hose with a handheld sprayer attached. Look behind the wall where you plan to mount the shower and measure to assure there is enough room to install the unit.
Drain the water out of the plumbing system in the RV. Locate the hot and cold water pipes. Find a place in the line that allows enough space to cut the pipe and insert a T coupling. Analyze the route you will take from that location to the shower location.
Cut the pipe and insert the T couplings. Attach PEX pipe to the T coupling and route it to the shower location. Place clamps along the way to hold the pipe securely in place.
Mount the shower at the desired location according to the manufacturer’s instructions. Flush mounted showers require a large hole to be cut into the RV but other types can be installed by drilling holes for the pipes only.