I masked off all the areas that will receive pro-seal with insulation tape and the scuffed it up using a scotchbrite pad. I then removed the insulation tape and cleaned it all up with acetone.
At the drain plugs, I masked in such a way that there would always be a way for any water to reach the drain plug after the pro-seal application
Both skins scuffed and ready for proseal
Closer view of the filler cap area
A closer view of the way the drain plug was masked