How to stop slide topper from sagging?

I have a 19' long by 3' deep slide topper on our TT. I had my dealer tighten it after several camping trips as it did get somewhat loose. It is better but still collects water on one end. If it had been installed at a steeper angle it might have worked perfectly but then you run the risk of wind getting under it when going down the highway and blowing it off where the topper attaches to the TT wall. I also have the center cradle installed as mentioned in a post above.

If it rains and stops and I am not leaving for a day or two or longer I just bring the slide in to drain the water and move it back out. Easier than trying to find a fix or bring more stuff with me.