A joggler is a great way to mate panels together. For an outer skin I would fully weld it. Don't weld it all in 1 go or as you say will warp all over the place. the trick is to take your time & stitch it together in bits so you don't get heat build up.
You can just spot it together but you run a high risk of filler cracking later on. that's a disaster as you will have to prep & paint it again, plus it could crack again.
Once you have done the weld, if it does distort a little, use the panel hammer to get it as straight as you can, then use a fibreglass paste filler over the join & low spots.
It sounds like a real bodge way to do it, but I welded about 10 small plates in the boot lid if my Ghia about 4 years ago & it distorted. I used a skim of glass over the bottom section before I did the filler work. I saw the car recently & it has been sat outside for 2 years, The boot lid is still in good condition even though other parts are bubbling up.
It holds the rust back for years. As long as the body is welded right first, there is no reason not to use these products. That is what they were designed for.
