I made a pickup bed trailer once. Stole the idea from another trailer I'd seen.
Found a 77 F150 that was being parted out. Told the guy I'd take the frame, rear suspension and axle, and the bed and rear bumper. I torched off all the brackets I didn't need, notched the rails ahead of the bed and bent the two ends in till they met and welded a hitch on it. Instant trailer.
I put a shell on the bed so it more or less matched the Bronco. Luckily the Bronco was white, so it was pretty easy to paint the trailer and shell to match.
The thing was strong, but HEAVY. I drug it along behind a basically stock Bronco that had a 28 spline 9" so it was nice to have a spare 3rd member and axles. I had stripped the splines of several axles on another Bronco that I built up with a 460, so I was paranoid about that. Never needed the spares with the stock Bronco though. I also had a set of spare driveshafts for the Bronco mounted to the frame rails, which I also never needed. Another nice thing is to have matching wheels and tires, so that in a pinch you can steal a spare off the trailer. I never had to do that either.
It was fun for a while, but have I mentioned it was HEAVY? A pickup bed is quite a lot of sheet metal. And using a truck frame...that's just nuts. I would have been far better off building something lighter.
But it was cheap, and it only took a couple hours to make it into a towable trailer. Never did get the brakes working either...
Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker