We have an 04 213 and I have back issues. We made some simple mods to help with the support.
DH made some braces out of PVC with slots cut to support the metal frame of the sofa when it lays down so it doesn't "give" as much. Then we got some 3/8" plywood that we lay on the dinette top when it goes down to make the bed. We store that piece under the cushion of the one bench. That little bit helps to level the overall surface. Then we put the cushions down and put an air mattress on top. It's not perfect and I would prefer a regular bed, but it works. It takes us about 10 minutes to set up and tear down.
The parts are easily stored. We put the air mattress in a bag behind the driver.
We love our little "MinnieMee." She went to Alaska and back last summer. . . over 11,000 miles and never even hiccuped!
Dale