Your JDM is still gonna rust.

[85Kai]

Gal dipping is unrealistic. The RAAF used to do it with their Land Rovers. The cost was phenomenal. You could have several 86s completely restored to showroom condition for the same price.
I just fish oiled certain spots in my car. So far so good.

[dove grey 64]

late model mini mokes were galvanised from factory.
the heat generated from the gal dip will warp panels and areas that are boxed can explode.

[Matt]

Rust is one of those things, if u know how to weld and have the tools to bend the metal replacement, "most" items are easily recovered...

[K1W1 Simo]

The other problem you have to deal with is the manufacturing processes of the 80's. If you unstitched a panel from your ae86 you would find the joining parts .i.e. the parts spot welded together, would have surface corrosion, add to that 0.6mm panel and capillary action, your car has no chance. One solution would be to use a proper spot weld drilling tool, remove all of your exterior panels...roof, quarters, rear panel. Treat them inside and outside. Re-gig them into place and 'spot weld' them back onto your car. You can hand make new panels and weld them into your car till the cows come home, if you have no access to the rear of that panel when it is welded it will begin to rust straight away. Even if you pay $20 - 60,000 for a resto. I am about to do a rebuild on my tailgate. Every time it rains I have to prop up my tailgate with a broom and open up the window rubbers to let the water out. Ducktail is beginning to bulge around the rubbers.

[dove grey 64]

seam sealer is important but like you say if you cant get to the back of the panel and its left untreated it will rust again, thats why you should drill access holes so you can load it up with fish oil or cavity wax etc.
or go the other way and sikaflex panels on, all the cool kids are doing it these days (lotus to name one)
welding weakens the metal around the weld, the correct grade of sikaflex will hold the panel on as much as any weld will.