We happen to own one of the Fiamma add on rooms that My Roadtrek has suggested. We use it with our PW Lexor. My comments on it are:
1. It is well designed and well made - in my opinion.
2. It did not include a "barrier" between the bottom of the PW and the ground. Maybe the current ones do, ours didn't, so I had to solve that problem on my own. The other three sides are just fine.
3. It does take two folks to set it up or take it down - and it takes a little while. We'd never use it for an overnight. Rather, it really is designed for go somewhere and stay a while.
4. You do have to think about how you're going to transport it. In addition to the walls, there are the poles - not the vertical ones that are "built in" to a Fiamma awning, but horizontal poles. If you look very carefully at Fiamma's website, you can see what I mean. We pull a small utility trailer almost everywhere we go (the motorcycle and canoe also needs to go, you see) so transporting the "room" is a non-issue for us.
5. They are a bit spendy. But, some say the same thing about a "B".
6. One of the things we like best is the ability to go from screening to more "solid" walls when the weather dictates.
7. While ours is a "keeper", it only goes with us on trips where it's useful.
Call Fiamma. They have always been VERY helpful when I've called.
Cheers.