My trailer has been been subjected to 30 years of rust and is no longer fit for the road. I spent a couple hundred bucks on a newer-used trailer, a bag of bolts, new rollers, and a new set of tires.

For the most part it's heavy surface rust and everything is structurally sound. I've already stripped the wiring and the axle, so I don't feel like reassembling it so I can tow it somewhere to be sand blasted. What's the best way to clean it up for primer and paint? I have a decent angle grinder. Wire brushes on it? Sanding disks? What grit? Flapper disk?