Just south of where you liveAttachment 232993

I've owned 6 DP 350 hp to 500 hp all have averaged 7 to 9 mpg. Currently 2014 Dutchstar 40 ft 450 hp 7-8 mpg towing a Jeep Wrangler 4 Dr.

2006 Monaco Cayman Cummins ISB 300 towing 2015 GMC Terrain. I get 8-9 MPG cruising at 63-64 MPH.

UK Driving
 

We have a Winnebago Vectra 40ft CAT C7 Allinson 6 speed auto

We average 12 MPG (imperial gallon) = 10 MPG US

In Europe we're limited to 60 mph, but as the trucks are limited to 56 mph, so most times we stick with the trucks (we're in no hurry!!)

We tow a tiny Citroen C1 and our winnie hardly notices it!!

As fuel is 3x the price in the US, I drive with a very gentle right foot and plan ahead!!

2016 Thor Tuscany 45AT forty five foot diesel pusher
 

In gentle rolling hills, around 8.2 mpg @ 65 mph (I-65 Chicago to Mobile)
In mostly flat terrain, around 8.7 mpg @ 65 mph (I80 Chicago to Cleveland).
In mountainous conditions, around 7.2 mpg @ 65 mph (I-84 Boise to Portland).
Forty five foot motorhome with tag axle, always pulling a 2015 Jeep Cherokee, always using cruise control, especially to resume speed from a standing start (much more efficient acceleration).

I don't have a DP but do pull a 5th wheel with a 2013 diesel. The DEP fluid is not much but with a load I would figure in the cost if mpg was something you worry about. Big truck fueling stations have a DEP pump or if you are cheap like me buy it at Walmart. 12-13 dollars for 2.5 gal.

DEP fluid is more of an agrivation than much of an expense. Falls under politics as some diesel engines are exempt.

'94 36' Monaco Dynasty, Cummins 8.3 ISC, Banks Turbo U/G, Allison MD upgraded to HD, typical GVW around 35000 lbs. 7 - 8 mpg, cruising on the interstate at 70 -80 mph using cruise control mostly. Note: Soft tire pressures give better ride but can reduce mpg by 1 or more. Set a little higher can save 1 mpg. Tire brands can have a big effect on mpg too. Goodyears -harsh -1, poor, Michelins - smooth - +.7, good, Dunlops - smooth - +.5, good, Bridgestone - okay - 0, average, Sumitomo - smooth - +.5, great(lasted 72,000 miles). I couldn't get them anymore so I'm now on the Dunlops(made by Sumitomo).

Average about 10. Cruise about 65, ever since tire shop mentioned any faster really heats up the tires. No mileage difference pulling our grand Cherokee. Mid to high 9 if really hilly.

Deisel Pusher MPG
 

Dan,
I did the following calculation in 2016 when we were making our final decision to purchase a 40 ft class A.

Estimate 10,000 miles per year on the bus
estimate 8 mpg
Calculated 1250 gallons of diesel

Worst case 1250 gallons at $4.00 per gallon equals $5,000 for the year
Reasonable average 1250 gallons at $3.00 per gallon equals $3,750 per year.

We decided that the cost of fuel was not a significant factor in our decision when deciding on what type of RV to own.

If you are paying $12-$13 at Walmart for 2.5 gals of DEF you getting screwed. DEF at pumps $2.50-3.00 per gallon. Its a known fact that onboard MPG computers are very optimistic. My mileage about 7.4 towing a Suburban. 62mph seems to be the sweet spot. I hand figure my MPG also. Nothing wrong with discussing this subject. If you don't think people with high dollar coaches should care, that's your opinion. Cummins ISB 9-10, ISC 8-9, ISL 7-8, ISX 6-7, Detroit Diesel 4-5. Anybody claiming a lot more than above is full of BS.

Tucson,
It's not that I don't care about fuel cost the point is that it's not a significant factor when deciding what RV to purchase. The fuel cost differential between one RV and another is the point. If you have a 35 ft travel trailer the tow vehicle will probably get a similar MPG as the class A diesel and once you park the RV you are still driving that tow vehicle to get around at some what better MPG but no ware close to the 20 MPG or better than what the folks in the class A get with their toad.

Point well taken, but the original OP was some one curious about DP MPG. Maybe those people claiming 12-13 were including their TOAD MPG.

2006 36' tropical 300 turbo Cummins deisal 36000 mi. I get 8-12 depending on wind. Just drove 8000 mi. On our last trip. Maintenence most important.

2006 36' 300 turbo Cummins, tropical mileage 8-12 , depends on wind. Last trip 8000 mi. I run it like I stole it. Good luck