I went the same route as pflaming. I mounted the wood and all skid strips with the bed off the truck. I wished I had help getting the bed back on, it was a bear. It would be difficult to drill the mounting holes with the bed on. It can be a pain to get all of the skid strip bolts lined-up with all the mounting holes. I can't amagine trying to do it on my back.
I guess you can put it together off the truck, get three buddies to help you mount it, measure, take it off, drill and then mount it again.
hopefully someone else has an easier way.