Conestoga

A flatbed or step deck with a retractable tarp system that rolls back like a curtain.

A Conestoga is a flatbed or step deck fitted with a rolling tarp-and-frame system that slides back to expose the whole deck for crane or forklift loading, then closes to protect the freight from weather — combining flatbed access with van-like protection. ('Conestoga' is a brand name that became the generic term.)