Speaking of Herculiner, I just did the interior of my truck with it this past weekend. The stuff really works great. I left the areas around the drain plugs uncovered so I can just pull out the plug and wash out my truck. It would definitely be best to prep the paint in some way for its application though. Make sure you buy the Herculiner brand. All the other off the shelf stuff is crap. (at least everything I've tried)

John