I know these things aren't exactly fuel efficient or bought for that purpose but what sort of mileage are you guys getting with the camper on and is your rig gas or diesel?
taking speed out of the question. 2018 Cummins Diesel
If I get X mph empty, I would get about 75% of X with truck camper loaded. towing my 7x14 don't make that much lower because the size if trailer is smaller then the truck camper when you look at wind load. and I would get around 50% of X towing my 10,000 lb 30' 5th wheel.