I would definitely recommend gravitex... I have several friends that have used it with good success.. It is a rock solid undercoating and you can easily paint on top of it.. I picked up two bottles and the spray gun for application for about $28.00! I friend of mine that has used this in the past told me the two bottles should do the underside of the car easily.
This is going on the underside of my 72 340 Demon project. I have decided to wait till just before paint to put this on the underside of the car and the wheel wells.
It is a little more expensive at their web site... see link below...
http://www.tcpglobal.com/hokpaint/S...gravitex&SearchType=All&SearchSup=&SearchCat=
Check out the PDF link below for specs about the product...
http://www.u-pol.com/countries/en/downloads/tds/gravitex.pdf
Let me know if you have had experience with Gravitex and how your experience has been using this product...
Thanks,
Craig