Interesting, my 2nd gen tray is all welded too.
Might be a nz market thing. I noticed that the cab end panel and the wheel wells are a bit different to the ones i see on here too.
If anyone with a 1st gen tray could take a photo of where the bolts are i would appreciate it. I think i will probably weld the rear sections on, and keep the fronts removable for some undertray storage boxes