The last time I checked a couple of years ago, there was no difference between the cargo capacity between the F350 and F450 pickups. The difference was the towing capacity.
Note: I am referencing the F450 "pickup" truck. The F450 chassis (no pickup bed) does have a greater carrying capacity.
If you are looking at a large truck camping, be sure you check the weight of the camper. The very large campers weigh 3500-3900 pounds before you load fresh water, all your gear, passengers, black & gray water, etc.
By my estimates it is easy to have a total cargo (camper, water, passengers & gear) coming up to 5500-6000 pounds.
So "no you can't have too much truck"!