Just as a FYI, we took off from Lebanon, OR to make a short trip to Coburg, OR for service and I was thinking about this thread so I paid attention to the the fuel consumption at different speeds...something I don't normally do since only the long term avg for our whole trip is important.
Heading S on I-5, ideal conditions flat and no wind with Cruise set at 55 the rolling avg varied from 10.3 to 11.5. Coach wt is ~32,000 and we were pulling a 3800 lb toad.
Returning N on I-5 pretty much the same conditions but cruise at 63 the rolling avg varied from 8.9 to 10.1.
I think the speed was difference between N and S.
Regardless, in order to get our overall trip avg of 8.5 some legs in the 10 to 11 range is reasonable which offsets the 3.5 to 5.5 climbing hills and such.
I think you observation that the C-12 saw limited use in MH's they were very popular with in OTR applications with 750,000 to 1,200,000 miles between overhauls.
