Do a Google search on "CH 751 lock" to learn more about how universal this tumbler set is to the RV industry, and some different vendors who sell replacement upgrades (combination locks, round key locks). Most RV owners aren't too worried about it. With a large screwdriver you can defeat any of these simple paddle arm locks. You would have to come up with some sort of deadbolt to raise the security level by an order of magnitude.
Edit: I found this selection of many types of camlocks on the McMaster-Carr website. They sell retail, accept credit cards, and have no minimum (that I am aware of):
http://www.mcmaster.com/#cam-locks/=p2rgc7