Lemme guess, it looks like this?http://www.popupportal.com/index.php?topic=50236.msg385468#msg385468
As was mentioned earlier, if you put some weight (get the DW and kids to climb in there) in the extended rear bunk, you'll notice that it causes the rear wall to flex, bowing outward and the rear sidewall directly behind the door rocks away at the top edge of the door. You'll also notice that the bottom rearmost corner of the sidewall collapsing as well.
You'll notice that the 1" x 1-1/2" wall framing in your camper is stapled from pillar to post. Makes it easy enough to fabricate but those wire staples tend to work loose at the best of times, so it's pretty much inevitable that things are going to become progressively worse over time.
There's not a lot to the rear wall and it's not very sturdy. Short of pulling the rear end apart to beef it up, there's not much you can do about that, so if you're not willing to go all the way with it, about all you can do for that problem is try to avoid putting too much weight in the bunk.
Similarly, if you really want to address the sidewall issues, there are several things you can do to help alleviate the problem and deal with the enormous amount of stress in the rear sidewall section. All of them involve opening up the wall to reinforce the joints and properly anchor the metal wall brace (there should be a metal angle iron frame inside the wall) to the floor and the surrounding wooden wall framing. Finally, if you really want to go all out, you can use hammer in mending plates to stiffen and secure any wall joints. When you're reassembling the wall, you can also use PL Premium adhesive to glue the inside luan to the wall framing and staple it in place. Once that stuff cures, it's incredibly strong.
In your case, you'll probably find that the posts on either side of the lift post holes are held together on one side by a piece of sheet metal which is tacked on with staples.
Adding a second piece of sheet metal to the inside of the wall posts and screwing it in place, then doing the same thing to the outer piece of tin (inside the wall) helps prevent the posts from twisting under load.
Here's a shot of the opposite rear corner with the top section of the rear wall framing in place. You'll notice mending plates on every joint and tin is screwed to the posts inside and outside of the lift post "pocket". Also, you'll notice that the framing in the rearmost sections that fasten to the rear wall are framed with 1-1/2"x3". The endwall sections were screwed to the sidewall corners using countersunk 1/4"x 3" self-drilling screws and washers.
Additionally, the outer skin on the rear wall is only affixed with staples and the weight transfer may have caused them to pull out or pull through the tin. No worries, if you think it'll help, you can pound the staples back into the underside of the floor then screw a piece of 1" aluminum angle to pinch the bottom edge of the skin to the underside of the floor. The angle is cheap and I used one screw per 12" at both the front and rear of the camper.
Of course it's easier to do all this when the whole camper is apart and I'd certainly understand your not wanting to tear into yours to this extent but hopefully seeing all this gives you some insight, a better understanding of the issue and a few ideas that might be helpful. Again, whatever you decide to do, the best course of action going forward would be to avoid overloading the rear bunk.
More info and pics in my rebuild thread. Click the camera under my username to go there.