Well, If you are a furniture maker, you will definitely not have any problems with a subwoofer box. In a car, generally, a sealed subwoofer will owork best, exspecially if space is a consideration.
Basically the best materials to build sub boxes for a car would be these
1. Marine Grade Plywood (1.25" thicknesses are available so you wouldn't need to worry about doubling up walls) extremely stong, somewhat heavy. (expensive)
2. Finland Birch/Baltic birch plywood. Very strong, somewhat light. (expensive!!)
3. MDF, strong, heavy, very easy to work with. weaknesses would be resistance (lack of) to moisture, screws (if you decide to use them) don't grip too well.
I don't expect that you will run into any power problems, especially if you are keeping modest power levels. I would run at least 4 guage wire, even though it'll be overkill at this point, it'll be worth it when it's time to add the other amp.
If you want any help with deciding on dimensions for the enclosure, let me know what kind of sub you are considering and I can help.
Dave
