I'm not sure what other folks do (I've heard of all sorts of chemical treatments, etc.), but my experience with metal and painting (used to have my own painting and contracting company) led me to my solution.

The first thinbg to remember is that MOST rust is just superficial. If you let it sit for 5 years sure, it might be deeper. However, generally there is good metal underneath the rust, and you just have to get to it. That being the case, I used an orbital sander with 3 grits (100, 150, 220) and went over all the rusted parts of my 745t in waves. After the 220 I found I had smooth, silver metal gleaming and ready to be painted.

Unfortunately I ran out of time and figured I could just prime it the next week, etc. Mistake. It rusted again IMMEDIATELY, and I will have to do the latter two grits (150/220) again to prep it. However, as I stated it worked like a dream. If you don't have an oribital you should get one. You COULD use a disc sander, but unless your experienced with it you are bound to leave half moons and obvious markings in teh spots you sand. The orbital basically is a smart sander that works the sanding material around in a star-like pattern at high speed, preventing the half moons and markings from being made regardless of pressure applied.

If your rust is deeper you can use this method and then use some hardening compound to fill the area (go to autozone or somewhere and look for a big red can with a plastic cap. This is an epoxy/plastic goo that yoiu add a chemical to and then hardens. You apply it like window glazing, let it harden, and then sand it to a smooth finish. It works PERFECTLY to fill dents, etc., and allows you to actually build edges or reconstruct destroyed elements effectively. Body shops use this stuff when all else fails and the owners don't want to pay for new parts.

BTW, for undercarriage or really bad areasd there is a hardener with fiberglass in it that is a little stronger.

Good luck,
Rick