Here’s my solution for our 2018 320-CS. I’m 6’2” and 200 pounds. Over 
the last 362 days we’ve made several attempts to find the perfect 
solution, but this is the final product. Below you see 
three slats, and the support leg. At the bottom is where the leg 
attaches/screws into the main slat. This is storage/transport mode. When
 ready to deploy, simply remove the wing nut in the center enough to 
allow both slats to rotate 90 degrees.
Next is the view after the wing nut has been removed allowing both slats to deploy to 90 degrees.
Below
 we see the slats pre-positioned, with the two slats open to 90 degrees 
sliding onto the cushions, but under the two or four inch mattress 
topper/memory foam. I intend to cover the ends of the slats with some 
material that will lessen the chance of the edges of the slats damaging 
the cushions or memory foam.
Below is the finished
 product with two couch cushions off the hide-a-bed from our basement. 
This is proof of concept, but we intend to to visit an upholstery shop 
and get some custom cushions made. In the lower right you can almost see
 the support leg under the corner of the cushion. This allows me to 
sleep at an angle and I can now stretch my legs with room to spare and 
have my head lower in the bed than my wife’s head! I also no longer fear falling off the bed!
Here’s a better view of the support leg. It’s very sturdy. I weigh 200 pounds and can sit on this without fear of collapse.
It
 gets its first three night test next week. And FYI, I did this using 
materials already in the basement, except for a three inch carriage bolt
 and two wing nuts, which cost $1.16 at Home Depot. And since there are 
two cushions, the one in the center can easily be removed, and due to 
the wing nuts, the slats allow for easy movement of the leg and slats to
 get access to the cabinets. The bottom cabinet is where we keep the 30 
amp and extension cord. The top is storage for blankets or other stuff 
that doesn’t require frequent access