I have to wonder if "something else" is going on. Your fuel economy WILL definitely take a hit at 72Mpg, but:
- JKU only saw a 1% drop with the same setup(? that doesn't make sense)
- Same 12Mpg at 45Mph (trails, stop&start?)
I would be OK with ~12Mpg fuel economy when towing. The killer is the size of the KL tank, but your trailer lets you carry extra. When I was towing with my Ram 3500 and a 5,500lb trailer, my mileage went from about 19Mpg down to somewhere around 10Mpg, and that's with my preference to avoid 65+ Mph.
I think there is a missing piece of the puzzle in here, but I don't think that 12Mpg should be considered "bad", all on its own.
I consider 12MPG bad because a vehicle I own (that should get far worse) gets much more.... My window sticker showed a highway fuel economy of 26mpg with a combined 22mpg. This is the first vehicle I have ever owned where I was unable to achieve those numbers. We are lucky to see 18-18.5 on the highway. Our JKU's ('13) window sticker showed 21 highway and 18 mixed. We had no problem exceeding these numbers, and even with all the mods get fairly close to them.
I have a real problem with adding a trailer (of any shape) that is less than half of the vehicle's rating and seeing numbers that are more than 60% of the stickered economy. In truth, I have an issue with the actual economy given what it's advertised for all the time, but seeing it get this much worse is literally heartbreaking.
I agree the comparison to our JKU doesn't make sense, It's my whole issue
We did plenty of trails, but I removed them from the average. The 45 was an average as well. It was on the roads in/around the forest we were exploring.
The trailer does have fuel, but it wasn't to make up for deficiencies with the KL performance. We often have times where a 350-400 mile range is needed. The ~18 gallons we carry are to extend our JKU to this. I never thought this wouldn't be more than enough with the KL.