Actually a combination there. The side rails drop in,,and the tie down rails are permanent on the side.
The really cool parts of the bed are underneath though. I was able to ditch the stock tank(junk and small), built a 36ga unit flush w/ the bottom of the frame, and then slung a semi truck air tank crossways in the back and tie it into a compartment which has my air hose(york onboard), various tools, the slide in ball mount..etc.
The winch works great for pulling elk in,,,sidehilling to the extreme..
The side rails hook together as a atv ramp too.