[slowmover]

I "know" a man from the Airstream forum who pulls this same trailer as analyzed above. A 1972 29' Ambassador being pulled by a 2014 Dodge EcoDiesel 1500 4WD automatic. 8-speed & 3.92 rear gears. As the owner notes, this option-loaded truck would be the least fuel efficient example.

On a certified scale, the truck weighs 6,280-lbs loaded for travel. The trailer weighs 6,650-lbs. (He notes that he is shy by more than 1k on trade capacity used). The truck weight is not quite 1000-lbs over what that 1975 Impala would have been with a couple of people and some gear. And it would have seen maybe the same 7-8 mpg as my folks 1976 Cadillac saw back in the day with a heavier Silver Streak. His Ambassador is fully rebuilt right down to new axles and dead-nuts alignment on very good tires (has an Airstream restoration business).

The owner of this rig (at 12,930-lbs) sees mid 14's with a well sorted weight distribution hitch while traveling two laners across Central Texas at approximately 65-mph. No cruise control. A recent 900 mile in state trip was at a hair over 15. The same rig but with an earlier Toyota Sequoia was at 8-10/mpg.

Overall, his Fuelly report is showing right under a 21-mpg average for all miles (21k miles). Highs to 30-mpg.

Most RVers aren't terribly interested in mpg. This is "a vacation" after all. Setting cruise is about the limit of things, and only then if on the Interstate. So comps against other reports of this same tow vehicle with a boxy conventional trailer have to be done line by line as to weights, travel speed and terrain.

As I'm at 15-mpg or better (much better depending on winds and traffic) with a rig which weighs an additional 4,500-lbs, it should be noted that I travel more slowly and am willing to work for highest mpg. When I purchased my 2WD manual trans one ton in 2007 (2004 model 305/555 engine) it was a clean paper purchase of truck and trailer to maximize mpg, not just longevity and reliability.

I searched for and found (in the south central US) just over a dozen examples of men with the same truck pulling 28-34' trailers of this type, where weights were 7-11,000-lb) and travel speeds were from 55 to maybe 65-mph. The mpg range was 14-16 which told me I was in the ballpark. These numbers were from mid-1990s Dodge Rams up to about 2008 with the Cummins. Later models suffered from emissions controls, and we all lost a bit of mpg with the changeover to low sulfur diesel (some of which can be re-gained with proper fuel additive choice). Post-2013 models should be back to this range.

No Ford was ever in contention on pre-DEF engines and only the earliest GM Duramax engines were competitive in that twenty year period.

Another Ecodiesel owner who spec'd for economy (2WD) and has a shorter, lighter Argosy (a short-lived low priced Airstream model) has seen as much as twenty (but without supporting data as to hitch set and Fuelly report). For both those rigs it would be great to have some A-B data of the same course run at the same speed both solo and towing. It's hard to zero in on the percentage change.

Now, there are those towing with more fuel efficient vehicles. And regularly seeing above 20-mpg where the TT in question is 25' or less. I chose these examples as trucks are popular, but not necessarily the best for mpg. (One might be surprised at the number of those carrying loads of firewood for multiple nights of campfires, ha! Or, like me, where truck and trailer are home.

The overall average is the FE number that matters. From the average highway mpg to the average mpg while solo. What's the fuel burn penalty for towing? I'm at about 36%. This trailer design shrugs off the wind problems and maintains a higher average.

It isn't all just straight line concerns.