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?
2015 RAM 3500 4WD MegaCab SRW Cummins TD with an Arctic Fox 811 (roughly 4200# loaded) we usually average 14-16mpg. I tend to keep it at about 62mph most of the time occasionally a bit faster. The truck has 3.73 axle ratio. I routinely average 19mpg unloaded. I am a very light footed driver, loaded or unloaded.