I know the following would be hard to visualize so I've included pictures.
The PO did not like the standard across the front sofa bed. So, she moved it to the Port side.
In doing so all that was left for a frame were two 1/2" plywood sides, a hardwood face and the pull out drawer along the bottom. There are also a couple of 1"x1-1/2" soft wood pieces stapled and possibly glued flush along the outside of the top edge of the plywood sides.
Also, and it appears this is part of the original platform for the sofa bed mattress, there are three lengths of rectangular aluminum tubing. One about 1"x1-1/2" runs the length of sofa just behind the front face and flush with the top edge. The other two pieces are more like 1"x2"X30". They rest on top of the plywood sides making them also flush with the top of the face frame.
The plywood sides are only about 1 & 1/2 foot long on each side. The sofa/bed connects to the 2"x1" aluminum tubes at the back end with "U" brackets. The back end of the side aluminum tubes are held "square" (I use that term loosely) by a length of aluminum angle bar the length of the sofa.
It appears that originally the angle bar was screwed down to something, which I assume made the whole set up far more substantial.
The problem now, well, the main problem, is that the aluminum side pieces are the only thing holding the heavy sofa bed onto the frame. Unfortunately the PO chose to only screw them into the edges of the 1/2" plywood with 4 screws on either side that only went in about 1". The first time we rolled the back over to use it as a bed the whole damn pulled loose and fell forward dumping my wife on the floor. After our initial shock we had a good laugh.
Unfortunately this was the second incident with this piece of furniture. On way home after buying the AS, the drawer came out and the ball bearings from gliders went everywhere. I replaced the gliders when we got home. We've strapped the drawer closed when towing since. The bed incident happened last October when we took a trip to Arkansas. Happily, we had our twin beds to sleep so no big deal.
We had to put the AS right into storage when we got home, our neighborhood and city have laws prohibiting parking RVs in front of one's home. We've just brought it home today. This is my first opportunity to fix it and we leave for a four month trip the in two weeks. So, I'm looking for some advice on securing the sofa. For now that's really all I have time to do.
When we get back this fall I'd like to do some interior remodeling and I'll be able to rebuild it completely.