I am looking to find the best rust preventative that is an oil based rather than paint or under coating. I have a lot of bare machined parts that I don't want to paint on the car. In my garage, that isn't heated, the temperature change builds a lot of excess moisture in there. WD-40 can't keep up.

 

Put some cheap engine oil in a spray bottle and hose everything down. Or just give up and paint the parts with a rattle can...

 

Something from LPS (https://www.itwprobrands.com/brand/lps) in the model shop.

 

Pour some new motor oil in a tin can and brush it on with a disposable paint brush.

 

I've been looking at FluidFilm. There are some decent Youtube vids of people reviewing it from the rust-belt.