I have the same problem Rob. I try to make sure I always run the outside tank until empty and then only use the inside tank until I get the empty one filled then go back to using it. One of these days I'm going to have to run the inside tank empty, but I sure don't want to. During the winter I use a 150 gallon external tank and bypass the smaller tanks completely so I don't have the problem very often.
2006 GMC 2500HD CCSB 4x4 Duramax/Allison, Titan 52 gallon fuel tank, Prodigy Controller, B&W Companion Hitch
2010 Jayco Designer 35RLTS, Cummins/Onan RV QG 5500 EVAP, Progressive Industries EMS-PT50C, TST Systems 507 TPMS, RV Flex Armor Roof