The plywood monocoque car guy

I know I haven't posted in here in about forever, and I'm (sadly) no
further along in this project than the "gathered most materials, still
doing last-minute-design" stage, but I need to ask a couple plywood
questions:

First, I'm guessing that marine plywood was used in the construction
of the Marcos line of cars because it was the best laminate wood
material available at the time (early '60s). The car I'm building will
be very much like the Marcos, in that it will be a multiple "stressed
box" semi-monocoque structure bonded at the sills and front and rear
bulkheads to the open-cockpit fiberglass body I'm using. In the year
2008, is there a another grade of plywood besides "marine" that will
do as well? The entire 1/2" ply bottom of the car will be epoxy-sealed
against moisture and rubberized for noise absorption.

Second, when you guys build (built?) monocoque small aircraft
structures of the stringer/skin/bulkhead type, what thicknesses of
plywood do you typically use?

Thanks for your kind tolerance!

Bart