I think it is preferable to install the wood boards with the bed off the truck, especially if you have added some items under the bed area that obstruct access to the bed strip bolts. Thats how I mounted my bed and it worked OK. If I do it again I would assemble it on sawhorses and leave all the boards and bedstrips attached but not tight. Then place the bed on the frame and line up all the bed-to-frame bolt holes. With the bed on the frame and measured square and with the bed-to-frame holes lined up, I would tighten enough of the bed strip bolts to keep the boards in the same position and then remove the assembled bed back to the sawhorses to complete tightening all the bolts. Its extra work but helps assure proper alignment when you finally place the bed on the frame. Even with the bed measured square if you tighten everything on the sawhorses first it would be possible to have the board bed-to-frame holes shifted and be difficult to install those bolts.
Mark
