A vehicle assembly includes, among other things, a cargo bed of a vehicle, a passenger side rail mounted to a passenger side wall assembly of the cargo bed, and a driver side rail mounted to a driver side wall assembly of the cargo bed. A crossbar is slidably coupled to the passenger and driver side rails. The crossbar is slidable along the passenger and driver side rails between a forward position and a rearward position. The crossbar is closer to a cab of the vehicle when the crossbar is in the forward position than when the crossbar is in the rearward position.