Eastwood's rubberized undercoating is what I used....7yrs ago. I bought the bulk cans and their profesional spray wand and used a compressor. I taped and bagged off all the components and sprayed 2 good caost on everything inclusing the backsides of the rear quarters. I used 3.5 cans. I think they were 32oz cans??
I regularly spray underneath the truck in the winter as well.<----big help.
Here's what underneath currently looks like.
Looks like I didnt wipe all the wax off the rocker when I did it awhile back..oops.