I've been coating the underside of my trucks with WD40 with a hand held garden sprayer for years. 2 years ago I switched to Fluid Film and shoot it out of a cheap amazon paint gun. It works OK, but I usually microwave the FF first to make it flow a little better out of the gun. I was thinking of cutting it with bar and chain oil.

My question is, what does everyone else do - if anything?

I also do this on the trailer axles and rims.