POR-15 Help!!!

[Joseph Cianciotti <jmc987@earthlink.net>]

Help.

I can't get the old paint off the floors of my B.  The rust is exposed. 
But the paint won't come off with a wire brush or 3M pad on my drill.

Do I need to remove all the paint before I use the POR-15?

If so, can I use a paint remover like JASCO? 

And what happens to the underside of my car when it goes out the drain 
holes? 
Won't that create new places for rust?

Please answer as soon as possible as the interior is removed and this is 
my only set of wheels.

TIA,

Joseph
67 B Roadster