It's quiet easy to make a leather strap with a wooden cilinder on one end and a D ring on the other. Lay this on top of the door and close the door. there you have your hard point, the 'soft' way.

I live on an attic with a couple of very sturdy wooden beams, and I made a new frame around my waterbed from multiplex wood with a fair amount of strategicaly placed holes in it. Plenty of possibilities.