longshot

I done the same thing to my boat about three years ago. I had the same questions, and I went with 1\4" aluminum for the decking material. It was a little pricey but with the cost of lumber now it may not be much different. The benifit of aluminum is not much bracing is required. It will not rot, warp, or degrade in any way. It is also a lot lighter than marine grade. The drawback with the aluminum is that it is not easy to work with (cut, weld, etc.). If you have the tools or know someone that does you will not be dissappointed with it in my opinion.