Sir,
Without looking at the corrosion myself it's hard to say for sure, but from what you've said it sounds pretty severe. If you lived up here where the roads are salted every winter for most of the winter, I would definitely advise you to sell the truck for what you can get out of it. If the roads in your area are not salted, the deterioration won't be nearly as rapid.
I bought a '96 F250 in 2004 that was in outstanding shape with only 40,000 or so miles, but in examining it before purchase I noticed that the undercoating had been peeling off of the chassis. It was in too good of shape to pass up, but ever since I've had to try to keep ahead of the rust before winter arrives. I have the most outstanding rust preventive/killer available, in my view. It's call Corrosion X Heavy Duty, from the same outfit which manufactures Corrosion X for firearms. Once applied it doesn't need reapplication for a few years in the same spots. The problem is that an undercarriage on a truck has so many "spots" that there are some areas which require coating every year. It is a pain in the behind. It sounds like the problem with your truck is considerably more advanced than mine, so you have to determine how much time you want to put into the battle, so to speak.
Here are a few of the problems that develop from chassis rust:
1)brake and fuel lines. These will tend to go first. Depending on where the engineers placed them, they can be a royal pain to replace.
2)fuel tanks and tank bands. I've replaced one tank which rusted through beneath one of the bands a year or two ago. The bands and their connections are thin and won't endure a lot of corrosion.
3)oil pan. I have to keep a close eye on mine. The factory coating wasn't worth a whole lot, and when it started peeling off, the Corrosion X had to rescue the pan.
4)suspension fasteners, esp. U-bolts and spring mounts. Here is where corrosion eventually becomes downright dangerous if left untreated. I have a friend who drives to and from Michigan a lot, who was taking one of his trips when a corroded spring mount gave way, and that was it. The repair was way too costly to justify.
5)the frame itself. Frames are really stout, but rust will eventually take them, and then you're done.
I'm not trying to scare you, but I've been a DIYer on my old, high mileage vehicles for many years, and have learned that the only thing which actually ends the life of a vehicle is advanced chassis rust at critical structural points. You might have someone evaluate the damage with his own eyes who can give you the advice you seek.
One other thing: In my view something is wrong when wheel bearings wear out at that low mileage, especially on a Toyota. Wheel bearings are generally very long-wearing components.
Best wishes,
Andy
