I have mostly use pressure treated pine 2x6s .. cypress wood is also used. I did use cypress once 20 years ago, Got it in a trade so I don't know how much it was really worth?? I had the boat 6 years and the bunks were still solid when I sold it. Is that 4" x 8" lumber? Maybe check with a local saw mill for cypress. PT wood is not as good as it used to be it seems...