I'm not sure exactly how much it weighed, but the fiberglass topper I had on my old 2k Sonoma was at least a couple hundred pounds. Not only did it not cause my little truck to squat (I've hauled a heck of a lot more than that without trouble), it actually improved the ride and my off-road traction.
Unfortunately, it seems to have stiffened the bed to the point that any flexing caused my tailgate to come open, but that point became moot when I traded it in.
Unfortunately, it seems to have stiffened the bed to the point that any flexing caused my tailgate to come open, but that point became moot when I traded it in.