Rust! Anybody do DIY undercoating?

[ma4t]

Any tips besides moving to a state that doesn't use salt during long winters?

Here's the deal. I live in Michigan and we have long winters. They use a LOT of salt on the roads. My 2004 Mazda has some small patches of rust that I noticed when I was trying to take off my hitch. It's right there on the frame. I should have taken pictures. In fact, I'll probably take pictures of the other places once I get the stupid hitch off.

I got a grinder attachment for my drill and worked it off, then sprayed it with primer. That's the only thing I had.

Does anybody have any experience with undercoating?

m