We used these guys. I was really happy with them. They were careful to get measurements - to make sure it would fit in the slide out, understand what step up into the slide out was so it wouldn't be falling off the edge - I guess you can get different height feet if it needs to go over. The wall hugging model works great. I was very happy with the fabric. Not affiliation, just a very satisfied customer. Came in 4 pieces, well packed, easy assembly. Not cheap, but I think it was worth it. And it beats the heck out of the little jackknife sofa that used to be there!
http://www.glastop.com/rv-furniture-products.asp?id=70