We have a slide out cover for our 179---but, it is canvas. I don't know the brand or manufacturer because it came with the POd when we bought it used from a dealer. It works well-it does keep branches, leaves, etc off the slide out roof. We use a standard sheet rock bucket with screw lid for the "ladder" and it is easy to install. When it's wet, we roll it up and stuff it in it's storage bag and hang it on a clothesline when we get home.
I would say that it works a lot better than nothing, but obviously not as good as an automatic unit. It does require some installation/removal at each campsite and can be a pain if wet. It doesn't seem to flap in the wind. It's not pretty,but effective. I guess I would buy one if it was $75 or so.
Vann