I wasn't able to get around to the rust portion as I started grad school and moved to Michigan. I have been washing the the car and undercarriage pretty often as I have invested in a car wash pass. After this semester is over (May of 2022) I will be doing quite a few things to the 4Runner. First of which will be the rust, and may possible make a thread for those who are curious, as I feel my plan is pretty comprehensive. I don't really have the time, knowledge or tools/lift needed for a frame swap so I think cleaning up the frame is my best and cheapest option.
My current less detailed plan is to first make some cheap sturdy stands to place some jack stands on. Then sand blast the frame, and try to get the inside of the frame, with a pressure washer sand blaster attachment (~ $32 on Amazon) and then pressure wash it to get rid of all the sand so it doesn't get trapped. After it dries ill go around with a wire wheel (~$ 12 on Amazon), needle scaler (~$28 from harbor freight) and wire brush to get rid as much as I can. Then, wash it off again and let it dry before I coat the inside of the frame with either KBS's internal frame coating(~$35 a bottle for 150 sq ft) or EastWoods rust encapsulator (~$28 a bottle for 10 sq ft.). I then will begin using MasterCoats Rust Kit (~$103) which includes a rust reformer/metal prep, rust sealer, top coat and special thinner (which I plan on doing with a ~14 spray gun from Amazon). Ive heard several people recommend POR-15 or KBS, but I think this will work better as its industrial grade (what they use on bridges for ~15-20 years) in New England. Plus just the top coat alone (ag111) has held up better than other products in an oxygenated brine bath for a few months. Once Im don't with that I plan on adding another top coat/ enamel product like POR-15 Top coat or raptor liner (~$48 for two cans on Amazon). Finally, I plan on spraying the frame, doors and everything I can with wool wax black, using their spray gun(~100 dollars for their gun and a quart of wool wax black on Amazon). After everything, including tax, it comes out to around $450 for everything.
What do y'all think about a plan of attack like that? Its going to be a lot of work, but I plan on having it till she hits at least 300K (currently at 169K) and want something that I'm only going to have to do once, except for reapplying something like wool wax or fluid film.