I would imagine the readings on the meter aren't that accurate - is there any reason you'd have added water to the FW tank? If you're on a different angle than the last campsite, that might account for that discrepancy.
Did you leave your water pump on while traveling? As soon as there's an opening in the flow of water, the pump will kick on and if you had a trap disconnected from your sink and the pump kicked in, that could explain all the water.
Last - any vents/windows open even slightly? Was the door fully closed (does it close air tight?)?
I'd look at those first before assuming a leak - but dry up what you have, check door, vents, windows, tighten the trap and if you're in a rainy place, you'll know shortly whether it's something more serious. And good news if it is - you are still under warranty.