basically its two plates. one is keyed and inset in the frame of the floor of the camper. also in that plate i put 4 nodules at 90 degree's to the keyed opening. that way when the twist lock is in place it cant vibrate and spin back out.
the bottom plate has a pipe welded to it and a 5/8ths bar stock L shape with a bolt welded to it to stop the spring. the end of the pipe is capped with a hole through the center for the 5/8ths bar to ride through. in addition to this the pipe is drilled and tapped for a grease fitting to keep the spring assembly in fine working order.
the spring will continually try and push the keyed bar stock down keeping the key in the nodules in the top plate so it cant spin and come unlatched.