Which version of the Overlander do you have. They came in two styles, Twin and Double. The Double is like Texas Gal 61 has with the two fold out beds. On in front and one midships. The Twin has the two single beds midships and the fold out bed in the front. The center beds do not fold. If the front couch is still in the trailer you should be able to see how it works.
If not, the gauchos, as they are sometimes referred to, has table top extension slides under the bench part of the sofa that pull out to the stop. There was an extra piece of plywood under the bench cushion cut to fill the gap, the backrest cushion was laid down flat making a narrow, short double bed.
The table top slides are available from woodworkers stores such as Rockler and the construction is a fairly simple project.
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