Is it time to bid farewell??

In my experience, I would take a weekend and pull the box off, pull spare tire off and have a good look. I used a chipping hammer where ever there was rust. It takes a while this way, but it works way better than a wire brush and less dust too. Good idea to wear a plastic face shield, safety glasses and a dust mask so you don't eat the stuff. With the box off is the best time to replace the rear spring hangers and shackles. as you can easily repace rivots with bolts/nuts. Have a look at fuel and brake lines while your there. If the bolts for the hitch look bad now's the time too. Have a good look at fuel tanks...usually dirt/rocks pile up on the skid plate and the tank rots out from rust or rocks rubbing through tank. If you feel real energetic, after cleaning rust, you can paint everywhere with a good quality rust paint and a brush. About rust...if I remember correctly my buddy, who is a welder, once told me that metal will swell/rust to ten times it's original thickness.