I have one on top of my avalanche using the factory luggage rack cross members. It does create more wind noise in the cab. It probably decreases fuel mileage slightly, but I cant quantify it. If you put the rack on the topper not sure how much noise increase you would notice. I hope to mount lights, high lift jack, shovel and max traks to my rack, but just haven't got to it yet. I have carried the shovel, folding chairs, folding table, and misc other items up there though. I don't put heavy items like coolers up there. Comes in handy though...hopefully I can finish it out with the lights, shovel jack, and max trax in 2020. Those items could certainly become useful on a hunting trip if the roads get bad or snow comes in. Not to mention, if they are mounted up there, I wont forget to pack them and they don't take up bed space or room in the truck.
OH, I also saw a guy that mounted/used a solar panel on the bottom of the rack, and then had the ability to recharge batteries as well for lighting within the topper, etc (as long as the panel isn't being covered with cargo. I guess he loads it up for the trip, but once at a destination, the items are removed from the rack and the panel is then exposed to more light/more efficient charging of batteries.