If you are going to buy one of the ad a room for Fleet wood trailers I suggest you buy when you get with your trailer or try and get used.
You can try and negotiate a better price when buying new pop up trailer and maybe get it for 400-500 dollars. If you go an buy the part separately at Fleetwood dealer you are looking at paying 900.00 for the Fleetwood add-a-room deluxe. OUCH.
Best price For Fleetwood Deluxe Add a Room?
Another way to go is to try and find used. Some people may have bought the screen rooms and not find they are using.
This is the best way to go. You might be able to get in the 300-400 range if you buy used. try and buy locally as these are heavy and a killer on shipping.
If you do get used and are missing instruction some kind soul took the trouble to post the original manufacturer instructions- you can view here