Haven't attempted a second awning but want to offer a possible configuration with consideration of the slide. My coach has a slide in the middle of our manual awning and the slide out topper sidewall rail complicates matters somewhat. What the builders did was attach the awning to the roof and added extensions to the awning framing to clear the roof when rolled up. When the slide is extended the awning will roll over the slide topper roller so there are no corners to wear a hole in the awning.
Filled the awning up with rain water once (forgot to drop a corner for water drainage while out sight seeing) and didn't have any problems with the slide/awning contact but the awning tube had a inch or two out of round bow. Surprised it didn't collapse.
Original set up with the extensions and roof mounted rail.
I replaced the carbon steel extensions with stainless.
Base of the awning frame is attached to the coach just the same as any other awning.
What the set up looks like. Notice the bow in the awning? Have since replaced the tube.