They could very easily have all of the door locks using the same key, but that takes time to setup and train people to do it. Whoever is installing door locks just grabs the closest one on the self and installs it.
You can buy the lock cylinders and rekey 3 of them. The only probem is up need a special key to remove the cylinders. If your lucky you can find a locksmith that can do the job, but you'll most likely have to pay the stealership's inflated prices.
You could also re-do every lock on your camper to one key, from these guys.
Re-key My RV - FINALLY an easy way to have just one key!
One thing that you may want to do regardless, is change out the CH751 Cam Locks if you have any. How secure is your stowed stuff if everyone in the campground has a copy of one of your keys. Most locksmiths can supply keyed alike cam locks. When I did my storage compartment cam locks, I replaced the thumb latch as well. Won't stop the serious crap rats, but it'll slow them down some.