I think an RV water heater test could probably be done by just getting the camco electric water heater conversion kit. It's just a heater rod and all of the electrical connectors to hook it up to a l.p. heater by sticking it into the drain plug, but this test could probably be done by just plugging the rod in and seeing if it could melt enough to cause a short circuit. Someone else might know more about the rods that are having the problems though.
My kit was only about $75. I haven't had a problem with it yet but I haven't had my water heater empty since i've gotten my RV.