Not sure about your specific trailer, but one end of your HWH is often somewhere under your sink/kitchen cabinets and the other end is accessible from a panel outside the trailer. The end you want is under the cabinets, and it should look something like Lou's picture above. Check to see if you can see the 3 valves in his pic, close the winterization valve and make sure the other 2 are open. It sounds like the water isn't making it into your HWH, but is being bypassed around it by the winterization valve.
DO NOT TURN ON YOUR HWH ELECTRIC ELEMENT UNTIL YOU FIGURE OUT THAT ITS WORKING ON GAS.
If the HWH doesn't have water inside it and you turn on the electric element (if you have one,) it'll burn the element out. You can tell that by finding the other "outside" end of you HWH.
Look around and report back...
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