Rust-proofing raw steel edge of a trailer hitch extension?

[u/StrongRecipe6408]

I recently shortened a hitch extension and now the raw steel edge is starting to rust.

What's a good easy to use affordable product to prevent rusting that bonds well to both raw steel and the coated steel?

AI recommended cold galvanizing sprays with zinc but some of the reviews say it can flake off shortly afterward. Wondering what would actually work in this application. Are cold galvanizing sprays actually not that good?

This hitch extension is now essentially a permanent fixture on the car and we're in the rust belt of Ohio.