Any good suggestions for bottom coating the body and rear tub. I am replacing the 1/2 tub so I have a clean surface, I was planning on using 3M rubberized undercoating, possibly zero-rust. What should I do under the front floorpans, which still have the asphalt based undercoating, which is very spotty. Can I still get that stuff and just put another coat on? Any info would be helpful.