Give me an example...

Jfet wrote:
I am at 18,000 pounds on our diesel Isuzu NRR and I get about 10mpg if I go 55mph. This drops to 9mpg if I go 60mph. Probably 8mpg at 65mph.

Amazingly I could get 13 or 14mpg even pulling 18,000 pounds if I stick to forestry roads and go 30mph.

Atmosphere sucks.

Pretty unusual base for a Truck Camper, Isuzu NRR. Company here uses a Canter 4x4, but modifies suspension ect to get SUV ride

Downwindtracker2 wrote:
Ford has a nice 3liter diesel in their new Ranger, so they do have an engine.

Yes they are everywhere here in Australia and are used as Truck Campers or Motorhomes
Here is a Truck Camper on a Isuzu Pickup Truck similar to the Ranger

Downwindtracker2 wrote:
Ford has a nice 3liter diesel in their new Ranger, so they do have an engine.

Well shoot. Doesn't look like there's anything comparable in the US.

They have a small diesel in the current Transit:

http://www.ford.com/trucks/transitvanwagon/specifications/view-all/

Engine - 3.2L Power Stroke® I5 Turbo Diesel
Horsepower - 185 hp @ 3000 rpm
Torque - 350 lb.-ft. @ 1500 - 2500 rpm
Transmission - 6-Speed Automatic SelectShift® with Overdrive

Bedlam wrote:
They have a small diesel in the current Transit:

http://www.ford.com/trucks/transitvanwagon/specifications/view-all/

Engine - 3.2L Power Stroke® I5 Turbo Diesel
Horsepower - 185 hp @ 3000 rpm
Torque - 350 lb.-ft. @ 1500 - 2500 rpm
Transmission - 6-Speed Automatic SelectShift® with Overdrive

Same Diesel as in the Ranger. Interesting bit it cannot be upgraded to Euro 6, so it is dropped from the European Transit.
Current Ranger 9/10ths the size of an F150, so not a small vehicle

Only 270 miles so far with my 1998 caribou 11m the plate on it says 3450 pounds my truck 07 ram 3500 drw diesel "5.9" this was the year they switched to the 6.7 but mine being early year I got the 5.9. Anyway I drive 55 and pencil and paper calculations show 15.24 mpg. And I'm happy with that. I would recommend an 1 ton truck and dual rear wheels but that's just me.

I get approx. 12.5 hauling my 3200# Lance 830 on a 2500 hd silverado running 62 mph.

My truck is deleted/tuned, so does better than stock 6.7 of my era truck. True 35" tires, leveled, and pull a 4000 lbs of trailer. 11.5-12.5 mpg hand calculated (yes, my speedo is caliberated for the tire size) is the best I do with my setup.

We got relatively good mileage on our 6,000+ mile tour of the Pacific Northwest: between 14 mpg (at 65 to 70 MPH) and 17 mpg (60 mph) with our 2014 Ram Hemi 1500. But my popup camper doesn't have a bath or holding tanks, so it has a lower profile and less weight than what the OP hopes to find.

You could drive a Prius at stay at Motel 6, that would give you great gas mileage and a tiny bathroom also. I manage 12-14 MPG from 55-65mph with a diesel F-250 and an Arctic Fox 865. I drive right past Motel 6.