Prevting Rust On Rocker Panels

[polaris]

I have a 2001 Silverado common for rust on the rocker panels but is still in pretty good shape looking for opinions on what to spray on the inside of the panels. I have currently sprayed fogging oil in side the drainage holes hoping it would stick to the back side of the rockers to prevent rust. Plan on sanding the outside to remove the rust and undercoating for better protection than paint since living in a heavily salted area. Would like any opinions or experiences. Thank!