For sanding I used a "flapper" disk in my drill to get the rust off, I also used a wire brush that you put in a drill. For spraying I used an old fence sprayer I already had. If I were to do it again I would research "sandblasting", I think it would save a lot on time, it took me a few days to sand it down.
Yes, actually I was thinking to do sand-blasting, but the cost to set it up just for one trailer was to much. Wish I had one. Actually if I had a sandblaster I would do ALL my other equipment. The stuff I use is from the 40's, still work but a pain in the rear end. LOL I have a bottom plow from the 20's that I still use, I saw the same one I use in a Museum and was thinking to strip some spare-parts for mine.