There is blocking in the exterior wall over each slide. It is sheetmetal, I assume aluminum. I would want to get the exact location from Alliance.
We ordered our 310RL with toppers installed at Alliance. The tracks were screwed to the walls. While on a trip to the Outer Banks, NC, we had sustained winds of 25mph, with gust to 40 for 4 days straight. The toppers were flapping quite a bit, as you can imagine. Because of this, the screws were being pulled out of the wall and the tracks were coming loose.
I contacted Alliance for assistance, via email. I had a call back in less than an hour. Kevin responded via email stating the screws should be replace with rivets, since the holes were damaged. He sent me a link to a specific rivet company's website and said I should use exploding rivets. I replaced all of them last weekend.
So, my suggestion would be to skip the screws and go right to rivets. Exploding rivets will pull all of the material together and clamp everything tight.
aDPrivet.com
Made in USA. Available in colors. Watch some of their videos.