The check valve(s), (you may have two), however, are located on the back of the water heater, accessed from inside the coach. It’s possible a fitting or one of the check valves may have ruptured, cracked or otherwise been rendered faulty. Some of the cheaper, plastic check valves fail at a higher rate than the brass valves. But it’s impossible to know until you gain access to the rear of the water heater from the inside. A close inspection of all the fittings and connections will reveal the location of the culprit. Hopefully it’s just a leaky P&T valve, but don’t overlook the fact it could be leaking from any component at the back of the heater as well.
A worst-case scenario would be a ruptured inner tank, but that is unlikely on a relatively newer rig. After replacing the offending component, be sure to have the fresh water distribution system leak tested and the air cushion re-established on top of the water in the heater. Let me know if you need directions how to perform that procedure.