I have steps made with Trex decking board. Will this adhesive work with it, and if so, what prep step would be necessary?

You can use our Polyurethane Adhesive over Trex or any other composite decking. The only thing you would need to do is to make sure that the area is clean and dry when applying the glue. Since the surface on composite deck boards is course, you wouldn't need to etch the surface to allow for proper bonding.