Camper shells are covers for the trunk of a pickup truck. Their purpose is to allow more storage into the trunk while also not have them blowing off into the wind. I think these are great for aesthetic and/or roleplay purposes. They can be either another thing in the add-ons section of modifications, or they can be their own thing with multiple camper shell upgrades, like spoilers.
Here’s some pictures of pickup trucks with camper shells:
