With a cap we can put twice as much in the bed of the camper. A tonneau cover would be of little use with my truck that I use to pick up plants from the nurseries and transport bicycles and move furniture. I added brackets for cross bars and supports for hauling our two kayaks to the roof of the cap.
With caps the aluminum ones are light enough for one person to take off. With a full size truck a fiberglass cap can weigh over 200 lbs so I used a hoist setup to take mine off the truck initially. If my garage entry was tall enough along with the ceiling I would have mounted a permanent hoist and taken the cap off an on inside the garage.
Now I go to the dealer where I bought the cap who charges me $20 a month to store it at his place and he takes it off and puts it back using their forklift.