Sometimes the external shower causes hot water issues, but that usually affects the hot water in the entire coach and not just the shower. But still I would make sure the outside shower is not at fault.
Turn the outside shower on for hot and see if you get hot water there. Then make sure to turn off both the hot and cold knobs. As a bonus you can also use a Phillips head screwdriver and switch the knobs to the correct sides while you are out there.
Use flat piece of metal (little flat blade screwdriver, a butter knife, a nail file etc) to pop the center caps out of the shower knobs. Then use the Phillips screwdriver to remove the center screw and pull the knobs off and swap them.
