I know it is confusing to understand how the snap n nap works unless you tried opening/closing them.
I'll try to explain what I experienced on mine...
When the bed is out and you want to close it up, if I just lifted one side, the bed support would flex and bind on the opposite side. The side panels would need to have a tug on them so they wouldn't "lock up" I would have to reach the other side an give it a tug upward to keep it aligned. There were no cam followers in a track to keep it horizontal.
Just like a roll up garage door out of the track...
Once you pass the 1 foot mark, the weight of the bed/frame would bring it all in.
So with that said, you making something from scratch could add a track on both sides with some type of wheel/guide that would let you pull it from one point with an assist strap as you are thinking....
Hope this helps, didn't want to muddy the waters for ya.
Maybe some picks on TCM would help "see" the opening.
look for rear bed shot
