Rear wall of 5er detached from floor

I had a similar issue on our 2006 Keystone Copper Canyon Sprinter. The whole rear end panel was letting loose from where it was attached to the sidewalls to the point where it would be open over an inch at floor level. I discovered that the problem was that the end wall panel was attached to the sidewalls with a thin strip of metal on each side. When that piece of metal failed, the end panel just started pulling away from the side walls. As far as I could tell, there was nothing else holding that end panel on to the sidewalls. At least not from the floor to about 2/3 of the way up the wall. There was no way to replace that strip of metal because you couldn't get at it. I tried several different fixes (long screws through the end panel and into the side walls) etc. that didn't work. I finally fastened an 8 foot piece of angle iron to the bottom of the end panel and then fastened the angle iron to the trailer frame I-beams. That took care of the problem. Interesting problem to fix when you're on the road and you think your end panel is going to come completely off!