Lay two 96-inch boards on edge so they are parallel and 37 inches apart. Set two 37-inch boards between them so they are perpendicular to the 96-inch boards and so they are spaced 93 inches apart. The sides of the 37-inch boards should be flush with the ends of the 96-inch boards. Screw through the 96-inch boards and into the 37-inch boards. Use eight screws for this task. This frame will function as a shelf to hold one of the kayaks. Repeat this step three more times so you have four frames.
Set each frame on top of another so all of the boards are aligned. Position a 84-inch board perpendicularly inside each corner of the stacked frames. The ends of the 84-inch boards should be flush with the bottom edges of the bottom frames. Screw through the bottom frame and into the boards. Use two screws for each corner.
Screw the other three frames to the 84-inch boards in the same manner as you did in the previous step. Space the frames 17½ inches apart.