KMM:

Yep. Same on '82 SC. 

I think the current (or recent) Corvette has Balsa wood sandwiched in the floor pan. Good sound-deadening properties apparently.

...

Found this (see last picture):  http://www.autoblog.com/2008/01/14/detroit-2008-corvette-zr1-chassis-display/

 

Interesting. I was wondering about the choice of materials but I guess it makes sense.