Originally Posted by methern
dealership said this was normal....
Don't get me started.
I would look at the exit of your vent. Mine has a screen on it and it is located right next to the gravity fill port.
If I had your problem (I may; just never needed to travel with FULL tanks to find out), I would install a valve in the vent line.
The easiest way to do that is if you have access to the back of the vent outlet and a trip to Lowes for a correctly sized vinyl tubing valve.
Harder would be removing the gavity fill assemble and modifying it to add the valve to the assembly before reinstalling it. (This is what I would have to do in my case)
Or maybe buy a new port assemble with a locking door. That should keep the airflow from sucking the water out of the tank.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW