I use 2 products. KBS Cavity Wax comes aerosol with a wand that fits into a 1/8" hole and sprays 360 degrees. I also use Fluid Film for large open areas where I want a solid transparent or black film that won't wash off. Fluid film stays tacky for a long time (maybe years) unexposed. I've been using these products for a long time. I spray the door jams and entire underneath of my '96 GMC Pickup every fall with Fluid Film and it is in darn good shape, for being in Michigan with salt and road chemicals. I use cavity wax in the rockers, cab corners, tailgate. Both available on Amazon. Just took these cell phone pics and they are upside down.
Use after painting is complete.
