cchartier: I used a 4-1/2 inch wire brush cup attachment on a 10,000rpm angle grinder. If I was to do it again, I would use a heavy duty grinder with a larger cup, say, eight inches. Nevertheless, it did a good job of scuffing up the surface and removing rust, etc. There was a bit of detail work--corners, etc--to do by hand. The welds were ground down with an upright grinder with a small wheel to get into the 'grooves' in the bed. So, when it came time to spray, they were flat.
BushWakr: I think the photos speak for themselves…But, to sum up, I had to abrade the application surface, fill any holes I didn't want (i. e. all holes), grind the fill flat, and clean the bed prior to installation. I'd say the prep took about as long as the spraying.
I am very pleased with the look of it. It cleaned up the lines of the truck outside the bed in a way I didn't forsee. So, in terms of looks, I'd recommend it. We'll see how it performs compared to the drop in liner.