If you just have two doors, essentially each closing off the passageway forward and running athwartships, then I agree with the curtain suggestion. They allow air flow, can be shoved completely out of the way, are lightweight, washable, changeable, and never rattle.

On the other hand, if you have a fore-and-aft door that just closes off the head compartment from the passageway, and if there is room, then I like a solid door there. Not for privacy but because you can bounce off it in a seaway without being flung out into the passageway.