> If it sticks to POR-15, it may be the perfect undercoating...

Why not just POR-15?  That stuff is great.  I did my whole floor pans,
chassis, underneath of the body, and more on my beetle with it.  I can't say
enough good things about it.  If you get the right POR-15 it is not UV
sensitive either.

Check out some images at
http://homepage.mac.com/mikeyb/body_work_9_1_01.html  (Note:  No brush
marks.  It was all applied with brushes.  I didn't believe them when they
said it was a self-leveling paint, but it is.  My body shop buy dismissed
the claim also because he had heard that before, but he was floored by the
stuff.  Quite literally.  We painted a section of his floor with leftover
stuff to see how it worked.)

Mike