Callen Truck Camper Attachment

Not sure if same company out of southern CA
Web site https://callencampers.com/ shows a contact page. Apears company sold 2018 and hasn't made campers since. If you haven't might be worth trying to contact. Few pics but don't show how camper mounted, except one shows a piece of chain in front inside bed corner. Contact previous owner?
Typically shells clamped or bolted to top of bed rails.

I'm assuming truck bu lights, the camper blocking access to taillight removal. Dont know what truck, on our 01 2 screws each inside tailgate pillers, so possibly drilling camper for access.
Seen a few pictures of these campers mounted then inside built out with cabinets...hard to imagine doing so without ease of removal or blocking maintenance items

It looks like those are more like a canopy shell which are usually bolted or clamped onto the bed rails from the inside. You may have to move/remove some interior panels if the camper was finished out inside after mounting.