Ive used some hammerite underseal on the internal rear floor panels of my car. Due to my interior and car beiong white i wish to paint over the underseal. Can i do this? does it work fine or will the top layer paint crack as the underseal never actually dries, but stays tacky? has anyone done this and had any good/bad look? If i need to remove the underseal and just paint fresh white onto the metal surface whats best for removing underseal that has been on for about 1 week?