Class A vs class C

I just spent several hrs figuring out my MPG over 70,000 miles of driving. What I did was eliminate gen-set usage over 2 hrs per tank full such as storms like Sandy and eliminate readings where I was working on engine problems where there was excessive idling or driving. I was surprised at the findings. My M/H weights about 16,000 lbs fully loaded,is 33 ft long with one slide and has a 454 tbi with Thorley headers, free flow muffler, and CAI. I averaged 9 mpg over all. when I looked at the data what I saw was that I got higher mpgs for the first 30k miles by .5 mpg. I got better mpgs in the mountains than on flats because I think it takes less average energy to go up hill than downhill. Towing a 2800 lb Toyota Corolla made no difference in MPG's. The worst mpg was 6 and the best was 12.6. The worst average was in Alaska 8.3 because it was hard to stay in 4th gear because of the roads. The best was traveling back and forth to Tn from Ct on I81 again I thing because of the longer less steeper grades found in the west (10 mpgs). Most of my camping is dry camping and have noticed less mpg when my batteries are somewhat discharged (Alternator working harder). I usually travel with a full tank of water and ave 62 mph. I do have 225 /70 19.5 tires and don't know if that is affecting the mileage readings.