Plywood with a staggered overlap will be your best bet given your situation. Using pressure treated pine would be a teriffic waste of money as there's no strength in it. What do 1" and 1/2" sheets of plywood cost? Or you could do it with 3/4" and double it up. Again...stagger the over lap.

Thanks for the info. I thought about putting down double sheet of 3/4 outdoor plywood, but it just doesn't convince me. My crossmembers are 12 inches apart, which isn't bad. But I see that plywood breaking really easily.

Anyone of any place in FL where I can get hardwood at a decent price?

With 12" cross members I'd be all over this with plywood! Be sure when on both tiers of plywood that the seams are on cross members.

I have 2 oak trees got blowed over in my woods not more than two tears ago. About 24" dia. and the bugs haven't got to 'em yet. They're yours if you come to TN and get 'em! I wish I had a saw mill.

Do you guys think that the rough cypress used for railroad ties will work on the stepdeck?

Just found a local guy with african sapele. What do you think?

Here are a few pics of what the trailer looks like now..

Only a little hole. I would run it like that lol.

lol.. I'm sure DOT won't notice the little hole.

I suppose it could use a coat of paint.