Can this be used for floor decking for a utility trailer that is 6' wide x 12' long? There will be 7 cross braces.

Hello, and thank you for your interest in Trex. Using Trex outside of its design intent is not recommended. Despite this we have seen many creative applications using our product. With that said there are a few installation guidelines for the best outcome. 1) Trex should be installed onto joists spaced 16" on center for proper support. 2) Trex requires gapping of 1/4" width to width and an 1/8" end to end if installing above 40 degrees Farenheit for drainage and airflow. 3) Trex should be fastened with 2 Trex recommended composite deck screws at every joist placed 1" in from the board end and sides. I hope this helps answer your question. Thanks, Tori - Trex Customer Care Team