Truck and camper mileage usually goes where the wind blows. I once averaged 20 mpg over 300 miles across Montana with a tail wind (Ram 2500 2WD, CC, 6.4L Hemi). I’ve also averaged 12.8 with a headwind and 13.9 overall for a trip to western Canada and back from Georgia. This was with an Adventurer 80RB running around 2500 lbs loaded. A direct side wind will also diminish mileage noticeably.
Neil & Yoly
2016 Ram 2500HD Tradesman, 2WD Crew Cab, 6.4L Hemi
2018 Travel Lite 840 SBRX