Cut plywood to size of tub deck and screw down to the frame (Image 1). Using the specifications from the manufacturer, mark the dimensions on the plywood for the cutout (Image 2).
Next, cover the tub deck with cement board. Use scrap pieces on the top. Screw the boards to the deck with cement board screws (Image 1). Set tub in place (Image 2). Use a 1-3/8" spade bit to cut a hole for the faucet.