We have had the same problem on our Jayco unit. Lose half or more of the water in less than 100 miles. I took it to the dealer for some warranty work and mentioned this as an issue. I was told to just fill up when you get where you are going. Well that is great if you have water where you are going and even if water is avaialable it does not mean it will be easy to fill the tank as ours is a pressurized fill system (though it does have a "country fill" feature that uses the water pump to fill the tank just like when you are winterizing but heck you have to clear out the storage area, remove a large panel adjust valves etc then put it all back. It didn't even occur to me to check that out when we got our new trailer as our old one had a gravity fill. In any case after I told the guy unacceptable answer he said they would check into it and perhaps they could reroute the vent and or overflow lines. It seems to have worked as it worked ok last time we filled it at home.
