Here are the details, of the undercoating of my bus.
Before undercoat application:
I was fortunate to catch this need, before rust and corrosion had seriously set in, before it was too late.
There had been enough previous undercoat to last the past 30 years.
I treated what rust had just started, with an acidic application designed to neutralize such corrosion.
Also much time and effort was spent further in preparation, by rinsing, and peeling off loose undercoat, to get a good seal against the paint underneath. I failed to get any pictures of the underbody, besides these wheelwells, but it was all essentially the same.
After application:
Now keep in mind in the following pictures, that each wheelwell had not been rinsed, from some road dirt that had accumulated. Even though the tires are in the way, you can see the difference a thorough undercoating makes. Especially with all the magnesium chloride that is used on our roads now.
With all the nooks and crannies to fill, it took a whopping 13 cans of rubberized spray undercoating!
Also, it was not easy as well, since many times the stuff would drip off, or backspray against an object, and get in my hair, face, clothes, and on the ground (which would smear as I would maneuver around).
I highly recommend an old hat that covers well, glasses, coveralls, and dropclothes (old shower curtains work best, as their life is about spent anyway).
Gasoline removes the residue really well.
With a set of car ramps, a car jack, jackstands (the wheels have to be removed, for each wheelwell), and a drop light, it is not a pleasant job, but you'll have a great peace of mind when you're done, knowing that you're vehicle is shielded from the elements.