We converted this 5 panel door into a headboard for our king size bed.
The edge where the hinges were mounted was trimmed to a smooth edge. The top and bottom were measured to equal lengths and trim to square. 4×4 post were mounted to the top and bottom of the door which when turned horizontal became the sides of the headboard. The post were screwed in with 4″ wood screws and counter sunk and topped off with a wooden button.
The headboard has 3 coats of semi-gloss enamel from Sherwin-Williams. The paint and construction has held up wonderfully. The headboard does not rock or knock against the wall. It is very sturdy and attractive.