My $0.00002 of opinion, not advice, cuz i'm in the same boat as you.
A lot of people on this site have taken the sandblast approach with spectacular results. They have made the trailers really nice looking, and protected them at the same time. However, sandblasting (at least in my area) would cost about $180-$250. If I was to restore the trailer, that's what I would do.
However, I'm not restoring mine. My trailer was built in 1967, and used in the midwest since the mid-80s. There is flaky rust, but no rot. My trailer, in its current form will outlast pretty much anything on the road. Given that I won't be towing it more than a few times in the winter, the salt exposure will be minimized (and MI uses the most salt in the US).
My plan is to grind, wire wheel my way to fame. I'm getting rid of the flaky paint, do as good of a prep job as I can, and paint it with the most durable paint I can. Appearance is a distand second in priority to durability and function. My trailer will haul gravel and topsoil, my garden tractor, bikes, furniture, and still be able to go camping.
I would feel horrible loading up a restored trailer with gravel.
Like I said, just my opinion. Good luck. I say stick with the cheap plan. If for no other reason than to please the princess, and avoid further financial scrutiny in future projects