last time i checked (about 6 years ago) you could still get genuine replacement floor from nissan

cut the tray floor out of mine. Removed rear end assembly and supported rear of car by cutting a hole on either side of the cross member. Slung a fibre sling through it and hooked onto an electric gantry crane. Using a 5mm drill bit, followed the chassis rails and cross member lines, drilling holes every 50mm. Lowered the car back down again, using holes drilled through top of tray floor as a guide, cut the tray floor out in sections. When it came to chassis rails and cross members, used flapper disc on a 5" grinder, grinding till spot welds have been located and ground 90% back. Pair of pliers is all it takes to pull of the rest, ensuring you dont weaken the rails and cross members at all. Went for a 2mm flat steel floor in mine. Bear in mind however that the existing fixing height for the old tray floor is 20mm higher than the top lip of the rails. SECOND floor attempt had ends pressed up at 45-degrees, approximately 25mm from the edge. Inner wheel arches are rolled 2mm flat steel also. Fuel tank rear mount is fixed to the underside of the tray floor. Retain the mount from your old floor, bolt the fuel tank up to the front mount and mark location for rear. Also have to cut out access panel for fuel gauge sender wiring. Dont know about strength opposed to factory pressed tray floor, but certainly adds a bit more weight over the rear tyres.

Checker plate looks nice, but would increase the weight of your ute. Not that having more weight on the back would actually help the balance for handling...

I would get rib-pressed high-strength steel (like the original) from another donor pickup at the wreckers, and weld that in. Maybe even from a toyota or other small pickup.

PS, forgot to say, the twisted wire cup bruch have a habbit of eating throu the metal where there are holes or thin metal, so be carefull.

There was a photo uploaded a few weeks back of a yellow ute with some sort of tray liner, looked tidy as. It's somewhere in the pics

if its rusted and you are replacing it dont bother with a spot weld drill bit. just get out the 9 inch and go to town on it, obviously you want to avoid cutting through things like chassis rails and stuff. but you just cut along beside the rails to get most of it out then just grind over the top of the spot welds so theres no metal left connected and most of the metal should be able to just be pulled off

The wirebruch on the grinder works grate, i know just need some overols to protect from the wires.
I have no idea where you prob is in the tray, The drill can reach them all, that why i segested it.
If you could get one thats busted infront, maby you could replace it with a good second hand one??

in perth we might have a guy pressing up some stock trays

what if someone could relpicate the original floor,
or make patches with the correct profiles pressed into them?

Yeh cheers guys.
Kiri1 i am using (i think around about) a 2-3 grinder with a "heavy duty twisted wire cup" as they call them they are pretty much what you would use on a drill but a lot more heavy and rough. I tried using the drill technique and got pretty much no where :s i would get about 3-4 times the amount of work done with the grinder than the drill haha. Cutting out and welding new pieces back in is all good and well but i have heard the more you cut out the less original metal there is. Which weaken the over all strength. So i will cut the very worst bits out and just weld up over the others. :)
WARDY,
i think i will just patch this tub up get it on the road thrash it for when and what i need it for and then look for a much better shell and move on to maybe an sr or ca project.
Cheers