Only two things I have found to stop rust, a heavy coating of a good clean rust inhibiting oil or very very cold, dry weather....
Without one or the other chips turn into bubbles, then rust patches then holes...
Keep er oily! Once or twice a year a truck you want to keep needs a good wash, dry and oil... The oil needs to drip, if it doesn't drip it isn't the right stuff... Waxy undercoatings are only good for new vehicles and even then they usually clog drains and trap water causing problems...
Without one or the other chips turn into bubbles, then rust patches then holes...
Keep er oily! Once or twice a year a truck you want to keep needs a good wash, dry and oil... The oil needs to drip, if it doesn't drip it isn't the right stuff... Waxy undercoatings are only good for new vehicles and even then they usually clog drains and trap water causing problems...