Based on what I have dealt with, your awning that is all ready installed on the unit doesn't have much if any backer.
On my 5th, the 2nd time I put out the awning it began to pull away when I lightly tightened my safety straps.
Going up on the roof checking thinking the screws were loose, out of maybe 40 or so screws on 7 had hit a stud, the rest where in the filon.
Contacted the dealer, and they told me that's not a rare event and we just put in bigger screws, per Keystone, blaming it on power screw drivers set with to much torque. Searched online and I cant tell you how many posts have been made with a dilemma like mine. Bigger screws. I took a look at many videos showing how RV walls are constructed. If you have a TT, not a problem, at the top edge is a header on all units. 5TH wheel, not one header for such was seen. Hell even my side brackets the screws are put in at such and angle just to hit a skinny single stud.
Ok enough. I had since added 3 window awning to my unit, few to others in the park and one on a slide similiar to what your doing.
How- Located every stud or backing I could find. The rail they will give you has predriiled holes, but I added ones where each stud/backer point.
On the other holes I used deep canoe rivets, capable on going through 1/2" of wall and still grip. There trifolds so they spread out behind the filon and hold that way. People say your gonna pull the walls down. Nope, the areas that are secured will prevent that from happening and the others are strong enough it cant begin to pull away like my factory one did.