Dear hlapadu1

Hope you're well. There are lanolin-based sprays, that are "translucent", so will let you see if there's corrosion underneath. Lanolin is the oil in sheep's wool, that keeps sheep from becoming saturated. I do not know how often a lanolin-based product will need to be applied. Rubber-based materials are opaque and can trap water.

Another way to slow rust is to wash the underbody several times during the winters. On a day when temps hit 50⁰F, a wash will flush-away salt, sand, etc., but leave time for some drying.

I bought a driveway washer and turned it into an under-body washer. It is a T-shaped device with six spray heads and two casters. I reversed the casters, so that the spray heads point upwards. I attach a garden hose at the base of the "T", where there's a shut-off valve.

Water sprays upwards with considerable force and removes salt/sand from the underside of my "winter" car. I use the hose with a regular nozzle to wash the wheel wells.

I also have painted the bottom of the oil pan with Rustoleum paint. This seems to have lasted a few years, so should prevent "rust" pinholes. On the whole, I think paint - applied on a surface sanded free of rust and cleaned with a power solvent - will pretty well prevent rust, without trapping moisture.

If the paint fails, you'll see it and be able to clean-up the failed area and re-spray.

I gather some car washes have an "under-body" wash option.

Hope this helps.

Yours faithfully,

Spook