It can not be done. An antique Ferrari owner wouldn't even consider it. You can not separate a unibody, treat it, and put it back together in the same fashion. You can dip it, that's it. Period. End of story.

I think that having a car that is in better than showroom condition is something worth aiming for.
Achieving this may be a little harder.
The first thing to work out is how much do you want to spend, how much time do you have to invest and what you will have when it is complete.
Secondly,you have to be careful not go too far---I have a lot of reservations about stripping a car (any car) too far, as many of the panels and components are welded in a series of jigs and fixtures during manufacture, which ensures that all the suspension mountings, the holes for the doors, windows, boot (=trunk for the US) etc are in their right places and are the right size. If you go too far, the basic structure will lose its integrity ( it will twist and bend) and you could be in real strife when you re-assemble.
I say that you should go for it as its worth doing, but keep in mind what this and the other posts have to say.
Best of luck!

No chance of new 4 door sedan shells.

Sounds like you have the right attitude though. It's hard to move on from a "project". My original green one was "given up on" due to too much rust. I had it for 3 yearsand I had to replace a lot of metal on that before finally deciding that I needed to look for one that needed less effort. I found one in the trading post as a abandoned project. It's funny how when it's not your only car..that the "too much effort" concept goes out the window. This is how the costs and timelines blow out. On a few occasions, I've discussed using project management techniques to ensure that car rebuild projects keeps to timeframe and budget. Otherwise these things don 't get finished. This is why there's so many unfinished projects in the trading post every week.

May the force be with you.
Chris

thanks for your input guys. i was wondering wether you can still get new 4 door sedan shells from anywere. I doubt it but if so please tell me were and approx how much. My plan is to get the car sandblasted, see how much rust there is hiding away and depending wether its structural weld in new bits or bog it. if its bad i guess ill have to find another one. this is the third one ive bought and the other two were way worse. the first one had rust the size of a basket ball in the rear quarters which had been bogged over under chicken wire and was rusted all the way out in the water channels above the doors. the second one must have been in an accident as the front end had been rewelded and wasnt too straight. so ill just have to be happy with wat ive got. at least ive got a datto

I second that about the hidden rust coming to surface in an accident. My sedan that got smacked in the back "neatly" ripped right down a factory spot welded seam. Makes me wonder about the rest. But if I get hit by anything bigger than a Maxima, I'm toast anyway. So it is and so it goes.

Sandblasting is a good idea but concentrate on the common rust areas..sandblasting all of it will mean a lot of work.

I'd do the following:

Rain gutters
Front lower fenders (guards) inside and out.
Under the dash.
Under the radiator.
Inside and out of the back guards.
Pull out the Tail lights and sandblast/rust treat around there. Same goes for the indicators on the front panel.
Sandblast the sound deadening from areas where body panel sections are joined under the car. Water can condense and sit between the deadening and the metal and slowly rust things away. It's a good idea to fix that. When rust starts getting structural..For safety reasons, the car really should be crushed.

I imagine on a ute, sandblasting and treating the tailgate is pretty important. Especially if it's been cheaply repaired in the past.
Pull out all of the glass and sandblast around the openings, if there's signs of rust.
Tops of the strut towers.
Lower body rails in the engine bay.
The chassis stiffening bracing under the floor.
Sandblast around the front footwells if rust looks like it's there.
For the sills, Pop out the rubber plugs and squirt rust treatment into the holes, drive the car around the block a couple of times to slosh it around..then carefully drill a couple of small holes to let the solution out. You will fill those holes with bog.

Now remember, bog is your friend. Although not structurally great. It's better than using a mig or oxy for flat panel repairs..why? because the heat from oxy promotes rust by flaking off any treatment or plating that's been applied to the inner (unreachable) side of the panel. This is probably why cars are spot welded together, to reduce heat impact on the metal surfaces. Not to mention it's quicker and lighter than other alternatives.

You might not like my "the car should be crushed" statement above, but I saw a friends Mazda R100 after an accident once. The whole front of the car was ripped off. The points where it ripped where completely rusted out. It could almost have happened if he'd jumped on the brakes hard enough. The car was a semi show car, so it looked fine..but the cancer was waiting underneath.

Some food for thought.
Chris

At the momment im in the process of restoring my datto ute. Im finding more and more rust every time i work on it, so what i plan on doing is getting it sand blasted, then when ive cut the rust out, ill get it dipped in a solution that kills rust and coats all the metal so it wont rust.It will cost a little more but at least ill know it wont rust again for a very long time.

I think the smartest, cheapest , and best long term remedy would be to import a new shell from SA ,
Unpicking and rewelding is a MAMMOTH job leaving an unoriginal finish with a high probability of creating more rust alot sooner than the new shell solution

Yeah, I guess my reply was a bit negative.

We need to realise that any rust on a 1200, has surfaced after 30 years. The chances of many of us still having our Dattos in another 30 years time is not real likely.

The doombringers will tell you that we only have 20 years of fuel left anyway...

But if it brings you pleasure, and you feel inclined to cut open all of the double panels where there are problems, it could be worthwhile. But it'd be a lot of work, and in pulling anything apart you risk not being able to put it back together properly, or maybe just not as nicely as the factory did it.

When I stripped my car back for painting, the painter dude wasn't too impressed that I totally stripped the doors, inluding the rubber seal channels. It'll do a better job, but it means a lot of work for him.

So I wish you luck, but I'm letting you know from my experience, that it's really difficult to fathom the huge amount of work in a complete rebuild. And the amount of work is completely dependent on your skills and the size of your tool collection, and the ability to work with other businesses who don't want to do your work in an efficient or timely manner.

Chris

On the other hand, if you are going to do most of the work yourself ... maybe it's worth it. Rather than galvanise, just treat the rust, and paint the parts thoroughly inside and out (both sides of the metal).

In the US, we cannot buy new panels. We'd have to get them from Au or South Africa.