
Will a rooftop cargo box make mpg even worse than TT already does?
So this rig averages 10 +/- 1. If I add one of those decently large molded rooftop cargo boxes to the top of the truck cap, will my mpg get even worse, make no difference since camper is already doing a number on my mpg? I'll probably try it at some point as I already have it from a different truck but thought I'd get opinions. Thanks. Nevada US Highway 50 between Great Basin NP and Delta, UT.