It is very do-able...it would be nice to have a template for the cut-out & hole placement, however the fender can be used for that with some figuring. The first side will take you a while, the second side would go MUCH faster. You need to cut a fair amount away around the original wheelwell & drill about a dozen holes to slide on U-clips.
One thing you will have to deal with that you can maybe find or make something for it the top support. Once the outer wheel arch is cut away, it becomes rather floppy. GM made a bolt-in plastic filler that attaches the inner & outer parts of the bedside. It's a rather simple design...straight, flat with a couple 90* bends. A sheetmetal fab shop could easily make something for the job.
I would not let this work needed to keep me from purchasing a nice bed that I found. My Two Cents, Lorne