You can make a permanent bed, but it will be limited to 48" width. I replaced the twins in my Overlander with a bed on the curb side and a desk and drawers on the other. The desk was designed so that you could sit on the bed while working, then push the desktop back if anyone needed to pass by.
(definitely my short hair days...)
The desktop moves on 3 100% extension ballbearing drawer slides installed on their sides. This is not the intended orientation, so they are not nearly as strong in this installation as they would be on the edge of a drawer, but it saved about an inch in vertical space, allowing standard sized binders to sit on the bookshelf between the desk and the wheel well. The desktop has worked fine, supports a fairly heavy laptop, and is even more convenient than I imagined. The top stays in place while towing, too, using only the friction catch in the drawer slides.
The corner of the bed was "chamfered" with a 45 degree angle so that you wouldn't kneecap yourself going from the kitchen to the bath. The "joint" in the floor is a gap covered by a brass strip--there are three of them in this trailer so that you can remove part of the flooring without having to start at one end of the trailer to repair a piece in the middle.