The trim covers the lap joints and locks the boards in position to prevent separation on uneven floor. The trim pack consists of pre-drilled three-one/4 inch large best rails and corner moldings that attach to the raised mattress with incorporated screws. Make sure you raise the plastic on sunny days, https://gregoryrtyyz.wikicorrespondent.com/5505554/the_basic_principles_of_raised_wooden_garden_beds