A slidable room assembly comprises a vehicle body having an opening formed in an exterior wall, and a reciprocable slideout unit or compartment disposed in the opening and slidable between a retracted position and an extended position. Sliding movement of the slideout unit is controlled by means of a drive mechanism that includes two sets of cabling. The drive mechanism includes a frame installed about the opening in the vehicle body. The frame includes a header, a sill and two pre-assembled jambs. The pre-assembled jambs have a plurality of pulleys with a plurality of cables pre-installed inside the jambs around the pulleys. One end of the cables, attached to the slidable room, is pre-strung through a cable extension hole. The other end of the cables extends out an end of the jamb.