Here is a link from Jason that was sent to me about how many layer's a sub enclosure should be. This topic has been brought up several times and thought that this article would help some installer's with an answer to their question.

http://www.caraudiohelp.com/newsletter/fiberglass_layers.htm

I actually went ahead and ordered his two DVD's fabrication one and two to see just what he does.  I must say that they are quite good to watch, and it's pretty hard not to learn alot.  In my opinion they're a must have for anyone like me who learnt how to fiberglass by reseaching online.  He shows you the actual techniques along with the methodology, not to mention all of the preferred supplies/tools and where to get them.

     Thank you very much for the link.