Hey Duce the V-10 was a great engine however my old coach had the 2 valve version in a 30 ft class A I too suffered with a 6MPG however I was towing my F-150, if Ieft the truck home I would get almost 7 mpg. from there I started using a fuel system cleaner and MPG extender (Lucas upper cylinder cleaner) A few things I noticed right away, first was how smooth the engine ran at upper RPM, the other was HOW SMOOTH the generator ran and how easy they both would now start, plus my MPG went up almost a 1/2 gallon per mile, Being a retired mechanic I always opposed any type of additives however I know what we call Gasoline is no longer the same stuff. (especially if it sits for a few months) I got to a point I used it with every fill up, it also cleaned the fuel system.
I since sold my old gasser and bought a 2003 DP with a Cummins diesel which was NOT designed to run ultra low diesel fuel so I use a fuel additive (Diesel Kleen) to combat the smell that comes from running the B20 fuel at truck stops, not only does it change the smell but IT REALLY MAKES THE ENGINE RUN SMOOTHER AT IDEL, and much improved start ups, again with the main engine AND the genny.
I travel mostly out in Nevada and Arizona flat out thru the desert