Let me add another thought to this thread. IF...there is always an IF... If an internal fitting broke (not a fixture) but an inline Tee or elbow requiring the PEX tubing be cut and capped, you will want to use a Sharkbite Cap for that. It would basically just push onto the cut PEX pipe. That would solve a leaking problem until proper repairs could be made. This is a link. Basically the same price as HomeDepot but without the hassle of going to get it!
https://amzn.to/3ulSV1o
Remember, the plugs I previously mentioned would thread into one of the swivel fittings that attach the plumbing to the fixture. It seems we read a lot about the outside shower fixture freezing and cracking...these are usually found on the first camping trip. If it was ONLY the fixture that cracked, then these are the threaded plugs you could use.
https://amzn.to/3VCFPse
Always good to be prepared!
OH...while writing this a member messaged me about a potential specific problem. The question was...."If there was a leak on the hot water side of things, could the hot water be turned off...and only use cold water." I will share my answer since it is along what we're already discussing. At the back of the water heater (under the sink from inside) there are two water lines connected to the heater. Typically the bottom one is cold IN and the top line is hot OUT. Assuming the water is off and you drained the water heater (anode rode removal or by valve depending on the water heater OR used the proper drain line under the camper), then remove the cold water IN supply line at the back of the water heater and use one of the afore mentioned threaded plugs to cap off the swivel connector. This would stop cold water from entering the water heater and thereby completely take all the hot water plumbing off-line.
LOL...nothing more exciting than a cold shower on a frigid night!