I used a composite deck product called Veranda...available from Home Depot. Its a grey color, comes in 8' lengths, cuts like butter and has a wood-grain print on one side. I followed their directions as far as spacing and used carriage bolts instead of the bed strips. I didn't add any additional bed cross members and after a year it looks as good as the day I installed it. I have a picture in my webshots "Shoebox album" (pg 8). Hope this helps.
Dave