Slide outs actually seal at the top by using the weight of the slide. The rollers are out near the outside edge of the floor near the slide opening. The slide comes up the ramp and on to the rollers as it enters the main body of the coach. It balances on the line of rollers, till the weight offsets and the inside of the slide drops and the slide seals at the top first and then pulls in at the bottom. If the slide is light it will come in almost all the way before dropping down.