For the second bed (on the right side of the vehicle) I first needed to construct the base. This base sits on the larger folded half of the rear bench, which is two seats wide. Due to inaccuracies and a slightly sloping and soft surface of this folded bench it was difficult to get this base straight in line with the already existing bench on the left side (which only covers one folded seat).
This base I did leave more open, so that I would be able to access it to store content, even when the bed is covering it on top. But this also meant that the sides would be inherently less stable, as they would not support each other through right-angle mounting of the side walls. Therefore I put a horizontal bar at the top of the base, which would connect the front and rear walls and also would provide the support for the bed to be on top.
This support is also used to stabilise the bed board on top by fitting between two other support beams which form a grove into which this support bar can fit.
Now there are two beds usable in the MicroCamper. When folded, the bed boards fit behind the driver seat, as shown in the picture below: