I have used "Corroseal" for years both on cars and industrial equipment and it works. Do not sand blast, but knock off any loose rust with a wire brush. Apply "Corroseal" to rusted areas with a brush. Let it dry then apply sanding sealer and sand where necessary. I have used this on several cars I refurbished and have had very good luck with it.
I have been buying it from an industrial marine supple-house.