For my 1976 OD25: I assemble a wooden "fish skeleton" frame, as seen from the top. I made it from 2x3's lapped a foot and bolted together(use two bolts about 8 inches apart) for the ridgepole. Custom-cut for the boat's LOA. The mast (spreaders removed) rests on its side, antenna/electrical wire holes down, and is tied to the bow and stern pulpits and is stored under the ridgepole. The ridgepole is supported by vertical 2x3's at the bow, tabernacle, bridge deck and rear of the cockpit, all cut so that the ridgepole rests level on top of the boat. These vertical 2x3's are attached to the ridgepole using angle irons screwed into the wood on each side. This structure is then tied to the lifeline stanchion bases with 1/8th nylon line serving as guylines. These guylines are criss-crossed so as to provide lateral and end-to-end support against movement. Of course, there will be some "flexibility" to the structure.
"Rafters" made from 1x3 wooden lath, and run port and starboard from the ridgepole to the sides of the boat. They are attached to the ridgepole every 2 feet by tying them together using 1/2" nylon line long enough to have a figure-eight knot at each end (for easy disassambly). The rafter ties are passed thru holes drilled in the ends of the lath and sides of the holes drilled in the ridgepole. The rafter ties are tied with a figure eight knot so that they are tightly held against the ridgepole. The outboard ends of the rafters are custom-cut and drilled so that they can be tied with 1/8th nylon line to two 8 ft. sections of lath lapped and secured to the tops of the stanchions on the port and starboard sides to make up an outside "frame".
Extra precautions: Be sure heat-seal all ends of the pieces of line you make up for all the tie points. Be generous in selecting line lengths for easy knotting and tying. Use scrap carpeting to pad strategically. Use stanchion bases, the outboard "frame", boat cleats, lifelines, and bow and stern pulpits as tie points. In my case, I use a 15x30 poly tarp to cover the frame. It reaches about 1 ft. below the gunwales, covers both the bow and stern adequately, and allows for good airflow. The tarp is tied together fore and aft and to the cradle. I use a long section of 1/8th at the stern as a "shoelace" to tie the tarp closed and to provide an easy entrance to the cockpit. A plastic bag sealed with masking tape seals off the exposed masthead (whip antenna and windex removed) and prevents water from seeping into the mast during winter layup. Use 1/2 piece of paper towel to pass through and cushion all tarp grommets (both the empty grommets and the line tied ones) to prevent the wind from making those black gelcoat marks. Again, when the structure is assembled and tied together, it looks like a fish skeleton as seen from the top. It's a very sturdy structure and easily disassembled for summer storage.
---Pete on LI