There will be a valve on the blue line (cold) and one on the red line (hot). They can be tough to reach and it is tough to tell which position is open and which is closed.
If you are sure they are closed, then try opening and closing it again to try and get it to reseal itself.
Otherwise hopefully there is enough PEX sticking out under the coach so you can install a new shut off valve. I would actually do it anyway and then leave the valves under the show open. Then you will have valves that are much easier to reach when you want to drain the water lines.
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