Cable driven slide

You could angle a piece of plywood under the mattress

Thanks for the info. It closes nice and tight, we are just finding the slight head down position irritating, but laying in a different direction creates it's own issues.

I had a KZ Spree with a rear slide which was controlled by cables. It also sagged a little. On the positive side this allowed water to drain away from the trailer. It's normal for the cables to have some slack depending on the position of the slide. When you are putting the slide in, all 4 sides should make contact at the same time. As Ron said, get it checked out if you think the sag is excessive.

Ron gave you the correct answer.

Neither. The cables only need to be adjusted if the cable is too slack and you are having problems extending or retracting the slides. They are NOT for height adjustment of the slide itself.

Putting a jack under the slide is potentially dangerous. If your trailer should lose its support for any reason, the jack will cause sever damage to the slide.

If it were me, I would have the dealer look at it and have a certified technician adjust the slide for height. More than likely, they will do nothing and say the slight dip is normal.

Ron