Our main slide topper is 14 ft wide, and does flap in wind (OMG!!) and hold water if heavy rain. I went to a pool supply store, bought a 10 ft water bag (used to hold pool cover down), and a pool toy with those vinyl nipples. Cut the nipples off, small hole in water bag, good rubber cement to glue on water bag. Put aboot 2 gals of water in bag through main fill hole, pump up with small compressor, and stuff under the topper. Doesn't move in windy times, no flapping, and no water pooling. Total cost under $15. Yes, you have to go through the steps to use, and take out when moving, but how it works is worth it!! Trailer is now sitting on property recently purchased, slide out, and bag is still in position and holding air and water.
2016 Timber Ridge 280RKS
2003 Excursion XLT V10 4:30 Axles
DualCam HP 450W Roof Solar/320W Portable