Best rust dissolver and rust preventative

Once you apply a rust proofing product to metal, no paint I know of will stick to the metal. So if you apply a rust proofing product first, there is no point painting over a rust proofing product. If I was forced to pick between paint or a rust proofing product, I would pick a rust proofing product. Easy to apply, will run into areas you can't paint, etc. Regardless if you paint or not, the rust proofing needs to be done/touched up annually.

Same concept....remove as must as you can mechanically and spray it with some chemical rust converter. Follow the instructions on the products you are using. Then if you can't paint certain areas, just apply the rust proofing product of your choice. Those rust proofing products will help prevent rust, even if the parts aren't painted.

The basic steps to address rust are pretty straignt forward: (1) remove rust; (2) neutralize remaining rust; (3) protect metal. Where it gets a bit complicated is the product choices. (1) removing as much rust as you can is important - you'll get better results no matter what you do next. (2) neturalizing the rust will stop the rust reaction from continuing. (3) unprotected metal will start to rust again. Paint + rustproofing product or just rustproofing product are the choices. The effort/cost you put into this depends on what you entend to do with the truck. Lots of posts on here of trucks where the frame failed due to corrision because the frame wasn't shown some love.

As mentioned above, you'll get a lot of opinons on the best way to go about this. There are a lot of threads on TW on this topic and the internet in general. The key is to do the rust proofing annually - stay on top of that and it won't be a rusty frame that keeps the truck off the road.

 

I don't know if it's still the same, but Por15 actually recommends top coating their products if it is going to be exposed to sunlight to protect it from UV. A lot of people have found success with painting over it.

I recall they specify to apply paint/primer at a certain point (when it feels "draggy?") OR if completely dry to scuff it before painting.

 

These frames rust from the inside out, you can apply every product known to man to the outside of the frame and it will still rust.

Noxudol 700 was what Toyota spec'd to be sprayed inside the frame rails and boxed sections for the recall that applied to these vehicles. Use Noxudol 700 in an aerosol can and a 3M 3ft spray extension with a 360 degree spray tip to do the inside of the frame, cross members, etc. Also when you do the rest of the frame, remove the spare tire and make sure you coat all of the metal frame surfaces you can get to, especially the one that runs above the fuel tank and the frame rail that it sits next to.