I have the gas 5500 and absolutely love it. It has 358 hours on it so far in just over 6 years. It lives on non-ethanol gas 99% of the time and I put Stabil Marine Formula in each tank regardless of ethanol or non. I also run it for 1 full hour/month with a load on it and I NEVER miss doing this. The oil/filter is changed every fall and the air filter was changed last year.
I have a bad enough back that 30 lb lp tanks are enough for me. I wouldn't ever want 40 lb and if that is the amount of lp it takes to keep the 5500 happy I will definitely stick with the gas version.
For filling the onboard gas tank I use a TeraPump TRHA01 Battery Operated 2AA Pump. It works great and is $20.00 on Amazon or it was when I bought mine.
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