Maybe if you get all the rust off first. Otherwise, the surface of rust protects the deeper layer. I did pretty good with Ospho. Same thing without the plastic coat. Since there's no plastic in it, you can apply as many treatments as needed to covert all the rust.I am a fan of Extend rust converter to start.
You do know that 70 MPH is pretty fast on a gravel road.I am definitely planning on treating and painting it. I am a fan of Extend rust converter to start. it turns the rust into iron oxide and acta as a paintable primer. I've had good luck with it before. I am going to tackle this on my vacation.
Tomko, As for your questions:
Do you have splash guards?
Do you ever drive on gravel roads?
Do you drive on roads treated with sand / grit / salt in winter time?
Do you ever exceed the posted speed limit (increases the force with which abrasives will impact your vehicle)?
Speed limit is 70 here which is plenty fast for abrasion to have an effect. I never thought of that.
This.Look into POR15 if you want to treat these areas. It is a three step process.
When my Tahoe was new I used POR15 to treat the entire underside. It lasted a good 10 years and only gave up because I never top coated it to protect from UV radiation.
I live in Portland, Oregon, a very wet climate 8 months of the year but no road salt usage. You wouldn't see that much rust on the average ten year-old car here. Salt is horrible to vehicles.This is normal rusting from exposed metal to air and moisture. Metal doesn't need salt to rust just air and moisture. There is a black paint from Rustoleum that you just spray on an it reacts with to coat it and stop the rust. Don't need to brush any of it off just get the dirt off and it will adhere.