Amcclaran, if you have a low water drain for your hot water and cold water lines, you have the piping already run to the outside of the camper. In reality, they are just extensions of the camper's water system. They are merely stopped at the very ends by valves.
As an experiment, find the low water drain for them (not the onboard water fresh water tank...that's a gravity feed line). Turn on your water pump, and open the valves. Does water come out under pressure? It should.
Your task would be how to attach hoses to those two low point valves and run them to a shower head. It should be easy if the camper was built where they are accessible.
Attached are photos of how I made an outside faucet (hot and cold) from my low point drains on my Arctic Fox. I washed my hands at gas stations with it, filled buckets, washed off the dog, and hooked a hose to it to wash the front windshield of the truck. You'll get the idea. The first two pictures show the water drain (Pex lines) and the cutoff valves. These are pressured and adding the outer valve allowed them to be opened and used like a faucet when the internal water pump was running, or when hooked to city water.