MPG. ?
 

I have. 2000 Monaco 40’ Dynasty GVR 32000# pulling a 2004 Jeep Liberty. I’ve averaged 9 mpg pretty much constantly. I drive 65 mph on the hwy. Don’t take off fast either. Cummins 350 ISC w/ Allison 6 speed auto. I also add a qt. of cheep automatic trans fluid at fill ups for lubrication for the fuel system. The low sulfur diesel fuel dries out o rings and it helps injectiors too. ( its oil , it burns.)
Guardrail 53 has it right. Maintain your MH and use it. Don’t let it sit for more than a month. MOVE IT.
Excersize the generator, A/C’s etc
Most of my driving in the Southern US.
PS.... I have an AquaHot diesel boiler system which has a small effect on my mileage. ( It isn’t running all the time).

With a lot of idling in the drive, and running the genny and aqua hot, 7.1 mpg doing 65.

One more time. Last fuel stop. 8.3 mpg, 65 mph.