Rust Inhibitors - Anyone used these Products

[68mg]

I'm looking for some type of rust inhibitor that will slow down the rust formation in hidden cavities like between the front inner and outer roof panels or the rocker panels. The KBS Cavity Coater and 3M Cavity Wax Plus both have long wands which I could put through the Visor Hole for the that roof cavity and that hole in the front of the rocker to do those. Are there better products for already rusty areas like these that you can't clean first that have these long wands or can be used with some sort of sprayer?

I did a quick search on this forum and found these products mentioned in this link being used during repairs when you can clean off the areas, but I haven't found anything about how they work with already rusty areas

http://67-72chevytrucks.com/vboard/s...d.php?t=735737

These areas in my trucks don't show signs of rust on the outside, but I know there's rust in there and just want to slow it down.