My only suggestion would be to think again about using Trex. I don't care what they say it will mold and fade unless you seal it. I use 5/4 cedar decking. Yes, it may take a little more upkeep over the years, but you can't beat the look, and if you need to replace a board in the future you can make it match with your older boards perfectly where not so much the Trex. And that's assuming they will still be making what you bought in a few years. Plus, it will save you a bunch of money to boot. The initial cost of Trex will not be made up over time because it is NOT maintenance free.