camper shell

A camper shell, sometimes known as a topper or cap, is a small housing or rigid canopy used as a pickup truck accessory. The housing is usually made of fiberglass or aluminum, and is mounted atop the pickup truck's rear bed. It generally covers the entirety of the pickup truck bed, and is large enough to be used for camping purposes. Even though use for camping may have been its initial purpose, it now seems most often to be used for utility and storage purposes. Some camper shells are so large that they can overlap the top of the truck's cab.
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