The other day I dropped something down past the engine and into the engine/trans undertray necessitating removal of the tray to retrieve it revealing corrosion on the subframe from 8 years of Michigan salted roads winters. I decided I might as well fix it while I had the cover off.
Photos 1-4 in the collage are as follows
1. Corrosion as found
2. After grinding and wire brushing.
3. After application of Duplicator Rust Fix.
4. After 2 top coats of Krylon Rust Tough Protective high gloss enamel.

I recommend these products and hope they will offer protection for several years.

 

Glad you've got that under control. Every spring (when snow is no longer at the forecast), spray with water via waterhose to remove salt stuck on that area and also every metal underneath to deter rust

 

Another good product, one that has been on the market for a long time, is 'POR-15'.


(POR stands for "paint over rust")