>They don't use salt on the roads here so frame is still in good shape.
Anon spent a lot of time in the rust belt and learned a great way to kill and prevent rust.
Get a $15 quart of Penetrol from the paint isle at home depot, put it in a spray bottle you plan to throw away, and hose down the underside of your car. Don't worry about overspray on rubber bushings, etc.
It penetrates like WD-40, then hardens like paint.
Works great on restoring faded exterior plastic, too. Just wipe on, then back off.
Repeat every couple of years.
Cheap and the most effective thing anon has found.