Glad to see you putting effort into your trailer. Lot's of potential with a Fiber Stream!
You are seeing one of the critical weaknesses of this trailer. The
fridge cabinet walls and the kitchen wall are critical to the strength of the trailer. They form a center cross truss that holds the roof up in the middle. Normally, there can be some failure when moisture gets in, the floor sags a little, and the screws that go through the side of the shell into the wall section let loose. The shell will then bow out from these walls, the roof will settle, and the wall section of the
fridge next to the door will push the floor down. I've had two, and it happened to both.
With the kitchen wall removed, the problem is exacerbated, and this is seen in the bowing out at the bed frame and back of the kitchen cabinets. All the cabinets in our trailers are critical for keeping the structure sound. Unfortunately the screws through the fiberglass can be the weakest link. They were the quickest and cheapest solution during construction.
So, whatcha gonna do now? Here's my recommendation, having worked with fiberglass, wood and steel in cars, boats, trailers. Also, I got rid of every screw through my shell, other than the door and the vents. You've really got to get the sides pulled back together and stabilized. Without the walls and structure, the frame is doing all the support work for the trailer, and it isn't strong enough. You need a strong box on top, being the shell.
Step 1: Put the wall back in at the edge of the kitchen. They cut the wall off, which presents a challenge. Replacing the wall would almost destroy the kitchen cabinets. They were attached to the wall during construction, and the wall is sandwiched between the bench seat and the kitchen. I'd recommend removing the counter extension, removing some of the bench framing, and putting in a new wall similar to what was original. Keep in mind straight up and down is not straight up and down in these trailers. The walls slope out at the bottom making it wider at the bottom that the top. I've made my walls with a solid stock frame and 1/4" plywood on each face. The original walls were too weak. Mark out where the wall will go with masking tape, and you will need to drill some holes out through the fiberglass for proper temporary attachment. This will let you pull the bowing back in. I'd sand the fiberglass and use the adhesive listed, but after it's together, I'd add some fiberglass tabbing between the new wall and the fiberglass in a few spots.
You'll probably notice the wheel well has come de-laminated from the floor or the wall. When you are doing other fiberglass tabbing, you might cut the failed fiberglass and reattach the wheel wells. They also contribute significantly to the structure and need to attach firmly to the side walls and the floor.
I'd sand as well as possible behind the
Fridge walls with an angle grinder and glue those walls in place with new screws as well. You could do tabbing behind the fridge, or in other places to help the structure as well. If you want to see the issue compound, put an a/c unit on the roof! (Don't do it)
Once you are done getting the walls straight and attached, I'd remove the screws and patch the holes.
Regarding the front cabinets, once again the screws are a problem. I'd recommend sanding the fiberglass with crazy aggressive sand paper and gluing strips of wood to the wall. I used the screw holes to attach my pieces while the glue dried, then removed them and filled the holes. What made the cabinets really strong was the inner wall plywood. I put this plywood inside over 1/2" foam, and this ran from under the cabinets down to the floor. Basically a shell within the shell. I glued strips of 1/2" plywood to the fiberglass shell where my inner skin had joints/edges.
Some time soon, I'll try to post a link to the pictures of our gut and rebuild.
Best Wishes!