Since I really dislike bad information I went to the Keystone owners forum which I am a member of and did the research. There is a problem with the Retreat model leaking the last couple of years but it has nothing to do with windows not fitting. Apparently they have a gabled slide out that forces water to run to each end and the design at the corner cannot handle the volume of water that is directed there, allowing some of them to leak. Some dealers have attempted to solve it with mixed results. Keystone's position is the different TT's may have not all leaked for the very same reason and is treating each one as a separate issue. It is disappointing they have taken that position but not really surprising in the RV world. Some owners have figured out how to install a slide awning over the gabled slide out that has stopped the issue.
I, like JJBIRISH would like to know what dealer this is that is selling RV's they absolutely know will leak to unsuspecting customers and why do they continue to bring in a model that is defective if that is the case? Knowingly selling a defective product has liabilities and potential civil penalties. I would also love to hear the dealer managements position on this if the OP would care to share where he works? Frankly I don't think I could work for people who would knowingly pass off a defective product to their customers if that is what they are doing as suggested by the OP.