I use this cargo box whenever my family of 4 go camping. I'm able to load all the light and bulky camping gear and anything else that I can fit into it (sleeping bags, pillows, blankets, air mattresses, fishing rods, life vests, swim noodles, etc) and it keeps my tailgate free for the heavy stuff.
I did notice that I get less miles per gallon of gas when driving long distances but it's not that bad. I tend to stick around the speed limit when the cargo box is on my roof rack because of the extra wind resistance and I don't want to put excessive wind force on it and have it rip away. It's always tight and secure but I'd rather be safe and cautious.
The outdoor guy