I have an on board 5500 Onan LP genset. It works great however I am a convenience user. I do not go off grid often or run genset for extended periods.
I may do an overnighter here and there but in general I only run the genset for a few hours at a time.
What you are proposing is a feasible idea. But it really depends on how often you plan to use your genset If you are looking to run genset all day for days at a time. You will need to haul lots of gas to remain off grid.
I think solar has become a better solution for those looking to remain off grid for extended periods.