So today I went to HD again to chat one more time , they stated ALL Trex is only coated on 3 sides and Trex's view point is they don't do the bottom because the boards have to off gas when they get hot . Yeah OK that's possible . Then we talked a product called Moisture Shield Vantage which is some super duper encased on all four sides composite . Per the guy behind the " pro desk " it is the only product certified for salt water exposure on docks . OK that's great but I'm not building a dock
Anyway for 80 boards 20 ' long it would be $4400.00 and then have to purchase the hidden screws/clips ! Then I drove to a local lumber liquidator I have used in the past . They sell Trex and their price on the 80 boards 20 ' long of the Trex Select with the install screws/clips is $5259.05 including tax .
So I'm tapping out on composite , my research shows there are too many negatives to offset the cost . I will go with # 1 grade PT pine and be done with it .