What I did with my CLC's was to take the left over trimmings from the deck(after it has been attached), cut them into 2" wide strips. Then I cut them into sections that would fit snug under the deck about every 15 to 18 inches.I used these to make ribs that fit under the deck. To size the strip, lay the strip on top of the deck and mark the ends for a good fit. Deduct about and inch and a half for the deck shear clamps. Just spread thickened epoxy on top of the rib and slide it into place under the deck. What this does is to double the thickness of the deck every 15 to 18 inches with a rib of plywood. - Hope this helps.