Position the two 48-inch boards on edge, parallel, with their outside edges 30 inches apart. Lay the plywood on top of the boards so the 48-inch edge of the plywood is flush with the outside edges of the board. The ends of the board should be flush with the 30-inch edges of the plywood. Screw the plywood to the boards using eight screws for each board, and space the screws 6 inches apart. Be sure to place the screws ¾ inch away from the 48-inch sides. These boards will support your jet ski.
Lay the 30-inch boards parallel, with their outside edges 48 inches apart. Set the plywood with the boards on top of the 30-inch boards so the 48-inch boards are on top and the 30-inch boards are underneath. Paired boards should be perpendicular to each other, and the 30-inch boards should be flush with the edges of the plywood just as the 48-inch boards are. Screw through the plywood and into the 30-inch boards. Use eight screws for this task, space them 6 inches apart, and screw them 1¾ inches away from the 30-inch edge. The 30-inch boards will provide overall support to your PWC stand.
Drill two 1-inch holes through the 30-inch boards and through the plywood they rest on. They should each be 2 inches away from and between the 48-inch boards, as well as along the 1¾-inch center of the 30-inch boards. Bolt the wheels to the 30-inch boards so the wheels are underneath the 48-inch boards and the plywood.
Fold the pieces of carpet over the 48-inch boards so they are completely covered. Staple the carpet to the boards so there is a staple every 6 square inches. Your stand is now ready to support your jet ski.