i've just returned from a 3000 mile trip pulling my 29 foot fifth wheel,(12500lbs) after testing mileage with propane on and getting around 11, 11.5 mpg , i turned the LPG off for a few fillups . i was really surprised to find my mileage only dropped around 1 mpg..... so my conclusion is not to tow with propane, it just uses it with very little gain. i used about 50 gallons in 3000 miles....... but running empty is another thing---- 24+ mpg w/ lpg, 17, w/out
so i guess more testing is needed

 

I just finished about 2,600 miles without propane and averaged 11.5 mpg. I was only driving about 58-60 mph though and when I drive at 65 mph I only get 10.3 mpg.

I pull a 28 ft 5er and gross about 19,000 lbs. It would be interesting to try propane but cost is a factor to consider. I am more interested in the hydrogen system but they are even more expensive.