Took me a while but I just finished spraying the undercarriage with Corrosion Free.
Took some time to prep: pulled the rear wheel well liners, dropped the spare tire, pulled off the mini-mud flap things (rock skits or something?) and then went to town.
Got the stuff sprayed in the 'wheel well within a wheel well', all under the truck, in most of the frame openings, through the bed braces, rocker panels, door bottoms, etc.
Anything to help keep the rust away as long as possible. Truck hasnt seen bad weather yet so that helped, even though it was built back in September of '16 there was very little surface rust (except for the driveshaft). Hopefully this will help keep it that way, and Ill only need to do a quick touch up spray every year now.