Typically if a check valve starts leaking it will leak back out through the city water fill fitting. Your coach also has a pressure relief valve plumbed into it next to the pressure regulator. If you will look to the left as you look into the trunk you should see the bell shaped pressure regulator. On a short branch line near it will be a 90 Deg cast fitting with a flat top. The label on the top describes the pressure relief. It is fairly common for these to leak unprovoked. When they do leak it will come out under the coach through an overflow tube attached to it. The common recommendation is to remove the relief valve and cap the branch line. The relief valve is redundant to the relief valve in the water heater.Charlie