I'm making a built in bookcase out of 24" wall cabinets set on a 4" platform. I will need to add a small spacer on the right side because it will be up against the wall and tough to open the cabinet without it. To make it symmetrical I was planning to add the same spacer ( 1.5" ) on the other side for a total length of 51" . The wall has a thin wood paneling on it and there are a couple of holes from previous a/v boxes so I was going to add a plywood backing to the bookshelf portion. My issue is that the backing would need to be 62" x 49.5" so there would have to be a seam. Do I split the 51" bookshelf into two smaller ones and hide the seam behind where they join? Or should I keep it as one and hide the joint behind a shelf? While I am at it. ... If I go ahead and keep it one open bookcase do I need to use a small cleat along back for the shelf to sit on or can I just screw through the backing into the rear of the shelf? I definitely plan on using some 1x2 to trim out the face as well.