My 5500 will burn about .6 gal/hr. Slightly more if using a/c "some", but pretty consistent 18 hr burn time on 10 gallons. My built in tank is 10 gallons so it is pretty easy to know what the exact fuel burn is as long as it is completely full in the beginning.
Total hours on the 5500 so far - 329.
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