Just did my first serious travel day with our "new to us" Challenger. The V-10 gasser did great and I ended up getting 7.7 mpg. No wind, not running generator, and pulling aluminum trailer loaded with Harley Trike.
I suspect I could see close to 8.5 mpg under similar conditions without towing anything. MH still only has just under 3,900 miles on it so probably not broken in yet.