Yes the salt eats everything no matter how often it's washed. I don't know how people can spend 30-40K on a vehicle and drive it in the snow, knowing it'll be a rusty mess in 10-15 years. Many people have two cars each, a good summer car and a winter beater. Wife has an '06 fusion that only gets driven in the summer and it's immaculate, but her daily driver '10 escape is rusting away. I bought my '98 in 2001, and foolishly drove it for a few winters when I was young and broke. Just those few winters was enough to do some serious damage.
The problem areas I've seen are:
Moisture gets into the torque boxes and eats the body mounts, which are not painted inside, just primer.
The floors under the roll bars are just primer as well. Water seeps under the roll bar mounts and eats the floor from the top down.
The rear cross member under the tail gate has huge factory holes on the bottom that lets water in to attack the rear body mounts.
Water collects in the bottom of the tub B pillars next to the roll bars and eats everything from the inside out. Floor/rocker/pillar.
The wheel wells of the front fenders have reinforcement plates that collect moisture and rot the top of the fenders.
Water will seep into the floor to rocker seams and rust.
There is no paint under the door or tailgate hinges.
The middle of the frame doesn't have drain holes, so it holds an inch of water and rots the frame from the inside out. The outside of the frame will look good, the inside is falling apart. Common areas are rear lca mounts and the center skid mountings.
Any hidden boxed section is not painted, just E coat or primer, with insufficient drain holes. If water gets in it'll rust.
Areas I found that are not too bad:
The large boxed A pillar section (behind the "jeep" stickers) had hardly any damage.
The firewall, cowling, grill and hood are ok.
Center floor areas, transmission tunnel, and the center tub reinforcement plate are ok.
Small boxed cross members under the bed were mostly ok.
The rear wheel well liners do a decent job of protecting all the seams and surfaces in the rear wheel wells.
As far as restoring a vehicle, this is my second attempt. The first was an old VW that I did a ton of body work on and repainted. But when Daphne needed a new frame and rust work, I had to pick the better project and the VW just had too many issues so it went down the road. What I've learned so far is THE BODY IS EVERYTHING. I don't care if the motor is seized, the axles grenaded, the transmission junk, the suspension sagging: if the body is good and clean then most of the work is already done. Also, whatever budget you've figured it'll take you might as well double it for all the little things like tools, small parts, prep supplies, etc that you find you'll need along the way. Figure out how much space you will need to do all the repairs, and once you start taking things apart you find you need alot more space to get it all out of the way while you work. Time: oh boy, it seems even the littlest thing that you think will only take an hour or two to fix ends up eating up the entire day. Easily triple your time estimate. And age? I'm late 30's, and after a long day of crouching, twisting, crawling, bending and reaching to fix stuff, my back and shoulders and knees are done. I couldn't imagine trying to do this when I'm 60 or retired. So if you want to restore a vehicle, it's a long tunnel and for much of it there's no light at the end, and I can see why so many projects falter and quit halfway through, so know what you're getting yourself into before you start.