Hi Mikegjax, we bought a mattress topper that has strong elastic. As you know when the slide comes in, the top mattress half should slide over the bottom. When operating the slide push your body against the bottom mattress to hold in place. The top with bedding should slide up and over. When slide is out just push the top mattress with bedding into place. Sometimes we adjust the bottom half to remove the "lump" where the two halves join.
Larry and Mary
Solera R 2013