on one of my past ute projects i completely cut the tub floor out, you will need a special drill bit for drilling all the spot welds out, not sure if you can do it with a normal bit.
Its a damn big job! but if you have the patience it would be worth it.
I also just measured up the floor area, went to a steel supplies place and got them to cut me some 16 guage sheet to size. Trim it up to suit and tack it in (was getting a mate to weld it in coz he is better at it then me lol)cut holes for wheel tubs and weld them in. Also from memory the standard fuel tank bracket is welded to the underside so you may need to reweld or relocate it.

As for being legal im not sure, you might be able to get away with it if it doesnt look too over the top, or just check with n engineer

I like your dedication, plaises rusted away, i agree, cut out and weld new pices in.
Do you wanne use the tray? I segest kleen with a wire bruch (on a drill) to remove rust and aply a quality eigeprimer (Plascon 1K) and paint with quality automotive paint.

Yes i am willing to spend the time on it and i think i will. i'm just about all the way back to bare metal. (the previous owner had just shoved a little bog here and there to fill an few holes. there was also like a house paint used on it very very thick and i even think there may have been some fiberglass bog used.) im going to try both alternates (melting brass onto the rust holes and also cutting the worst parts out and welding new pieces in and even just welding up the smaller nto as bad holes.) :)

Roadworthy i dont know, if rust is the only reason, i would segest an alternitive salution, cheaper? probliby (depend on the current damaged) Work? Have seen it done, lots of elbogease to do properly, Not impossable.

well mine has much rust with in it and i'm looking at just patching it up for road worthy but its rusted here there and everywhere and so i was wondering if anyone else had had any experience with this problem.. (same as you armiee) like don't get me wrong i would much had the original but its old dinted, rusted and looks horrible. :( so i would much rather it looking nice or at least reasonable. i was also wondering if anyone had done this and had to get it engineered or if roadworthy had knocked it back?

yeah im curious too, mines compleeetely rusted out, i was thinking of cutting it all out and replacing it with a pressed metal of somekind. or just leave it open for weight reduction hahaha

flat sheet metal tray has no strenth

Eddy, what is the prob with yours? Why do you want checkert plate and not the original?

Hey guys just wondering what people have done to there 1200 ute trays? whats involved with getting the bottom of your tray cut out and replaced with checker plate? is this a very big job? does this need to engineered and is it legal? Also would anyone have any idea of costs for this job? and on last thing would anyone happen to have photos from your jobs (if you have done this berfore....)
Cheers Eddy :)