I drive my 63 alot in the warmer weather. I put front floor pans in it and then just sealled them. I cleaned off all the loose undercoating and then painted the underneath with rustolium gloss black. I like the gloss black as it is easier to clean off if it gets dirty underneath from driving alot. If you scroll down on the link you can see the underneath on my 63. Ron

http://www.1962to1965mopar.ornocar.com/mmo82008.html