Built a bed, went back and fourth on a few designs I found online, Ended up combining two to make something that could close up into a couch and a bed lengthwise to maximize the living space and storage in the camper.
Ended up with slides for 2/3rds and a plywood framed backrest for the last end. Makes for a really solid couch frame and a really comfortable bed with the most support where you need it. Keeps it fairly light as a mix of 2X4's 1x3's and 1x2's. The feet are 2x4's supported by a frame of 2x4's. And the feet slide on the vinyl floor with soft pads for furniture. Cut up some Piano hinges to support the backrest and rear legs.
Attached the rear legs more centrally, and will be supporting the rear of the backrest with a 2x2 piece to keep it as rigid as possible behind the legs. the 1x3 frame is good, but likely wont hold too much weight or 2 people sitting on it out the back doors. (holds me at 165lbs fine, but there is some flex)
This evolved as I went and was originally going to put less supports and cover it in plywood, pretty happy how it is and lying on it feels really supportive and comfortable with 4 inch foam.
Ended up getting a tri fold mattress from Amazon. It was 59x80x4 for the size when fully expanded. I ended up cutting off 3 inches of one side to fit the 56 inch width of the trailer. The cover fits back pretty well and you actually don't really notice the excess from the cut mattress. This stuff cuts really easily with a serrated steak knife, not the cleanest cut but it works and is hidden in the cover. The original mattress edges are not perfect anyway.
Here is a shot of the back, I will be finishing the wood with a mix of fabric and aluminum edging. The legs on the back just hang for now. Might strap these in or use Velcro if they make any noise or anything when driving.
Inside we are left with a decent amount of living space. and this this is comfy as a sofa. Might get something to use as an ottoman/storage/table later on.
We don't have much room to spare when its folded out as a bed. But I am really happy with the design. I can pull it out in a few seconds to make an almost full queen bed. Its a little tight but setting it up inside with the doors closed is easy. Back to couch mode is a little harder without opening any doors. There is about a foot or room to put on your shoes and Ill make sure the dog has a bed at the foot that is part way under the bed to sleep (she is a little french bulldog and doesn't take up much space.)
So it's 4 inches shy of a full size queen bed at the end. I had a nap on it already and its comfortable! I might see about cutting out a little 3x3 square off the ends of the mattress and bedframe to more to make up for the sides and slide it right back to the door edge. This would free up another 3 inches at the front cabinet end. But I'm still deciding if this is needed and I dont want to lose any length if possible, we are both ~5'11.
Still have lots of storage space below the bed and lots of headroom, Thinking I might put some drawers underneath to keep things organized. Next is finishing the bed frame and cleaning up some of the rough work.
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