Would like to add a comment or 2 here. You really don't want to add any type of a room or structure to the Horizon on your Casita. The awning is not meant to withstand any amount of wind. It is a sun chaser & thats all. In the event of a wind you'll end up losing your awning. Even by itself a wind that comes up suddenly will ruin your Horizon awning. I've seen big heavy duty awnings on big trailers ripped right off the brackets & pulled out of the body etc. The awning on your casita will do the same, act like a sail & damage everything.
The horizon on your Casita is light duty, roll it up if you leave for the day. A stiff wind can come up in minutes. Once you add something to the awning it complicates rolling the awning up.
If you want another room or more enclosed space try the Screened in sun house. A 10 X 13 screened in room costy 39 dollars at Walmarts & goes up in 1/2 an hour. It weighs nothing & folds up to nothing too. It will give you lots of extra living space, keep the rain & sun off you & the due & mist too. And the bugs away too. And thatrs my sermon for today. Joe Manzi

Joe, I absolutely agree. And I'm sure the same holds true for the awning on any fiberglass travel trailer, although you and I are most familiar with Casitas.

I saw a fabulous “screen room” last summer, similar to, but surely not (from the price), the one you describe. This one was “gazebo style” and had not only screen panels, but also solid canvas (or, more likely, nylon) panels that could be zipped into it. Cool night out and those folks were all snug as a bug in a rug, with their screen room fully enclosed and their propane lantern for light and warmth. It was pitched over and around their picnic table, so I'm sure it didn't have a floor. I would think, though, it could double as a tent for the overflow crowd, if needed.

:sunny