So we realized that keystone blocked off EMPTY space under our sofa (see picture 1). We removed the brackets (which are attached by screws from under the sofa - must have been assembled prior to placement in the unit) and I pulled the fabric back and trimmed the board slightly so it wasn't too tight a fit when I attach it as a front to the drawer. Next I built a box to nearly maximum depth and width (leaving a little space at the rear for the cord for the air matress) and put furniture sliders on the bottom so I didn't have the hassle of drawer slides. Then I attached woodspacers to the old covering on the front to prevent the bottom of the drawer from being overly visible ( I used screws and liquid nails). I then attached the drawer to the spacers with liquid nails and screws. Finally, I added some black duct tape across the front bottom edge of the drawer (slightly visible in the last picture). The duct tape is important as it is a good quality indicator
and this also hides the bottom of the drawer. Tomorrow I will be adding velcro to hold the drawer closed during transportation. I was very happy with how this turned out as this has added substantial storage space in a totally unused area.