We have the same problem on ours. During a big rain storm and then a freeze overnight, we now have a much bigger sag as the topper material stretched out...the only "temporary "fix is to replace the fabric, which will stretch again. We now just put a small beach ball under the topper when we have the trailer at home as we do keep the slide out for long period of time as we use the trailer a lot as an office/school room. When we are on the road, sometimes we will put the ball in depending not he weather or we just pull the slide in about 4 inches and it will drain quite well.