[imack]

If you haven't built the sub box yet, then kona is right your best bet is a vacuum system. Apply the CF to the MDF (or whatever your using for the sub box), put some waxed mylar on top of that and then slide the whole mess in the vacuum bag. The mylar will give you a very smooth finish. If you use enough resin, you could probably even polish it afterwards.

If you've made the box already, then the vacuum bag is not an option, as the box will be tough to fit in the vacuum bag and would be crushed by the vacuum. In this case, I would suggest sandwiching the CF between the box and another piece of MDF, then putting weight (as much as you can find) on it. Again, I would suggest mylar for a smooth finish.

Here's some sites for vacuum bagging material and info:

http://www.acp-composites.com/
http://www.cstsales.com/

Ivan MacKenzie.