I do not believe its a mfg problem. I know my coach is a 07 diesel and the front door glass is foggy. This is due to just being old I guess.
The cost of a new glass for me is about $1200. I have read of two different methods to fix the problem. One is to remove the glass separate them clean very good and put back together with caulk and tape. Yes there will be not gas in the middle but to me its a trade off worth while. The second is a glass company replacing the glass with a single pain automotive glass.
If you are talking about the normal window glass can not help on that one. I would not let the glass be the issue between getting the coach you like our not.