If you're tall... Be wary.
Used to all the time. The only downside I found was in the late fall, winter, that steel truck bed got incredibly cold. You will want to have at least a 3 to 4 inch insulative foam pad under your body in cold weather or that cold steel will suck the heat right out of your body. Hypothermia can be a killer. Also make sure you have decent ventilation in the late fall and winter, otherwise your breath is going to condense on the inside of the topper and drip water on you all night.
Anybody here use their truck with a topper for camping? Ive been thinkin about picking up a used topper for my 89 dodge to start transforming it into my hunting/ camping rig. My thoughts are clean the bed and add a twinsize mattress, then build a full length roof rack to hold all of my gear.