Cabovers are for sleeping. Sleeping occurs when your eyes are closed, therefore you really don't need a window. When you wake up, take the elevator down to the lower mezzanine and look out the windows that are already there.
If you insist on moving forward with the idea and you don't know what you are doing, I would go to a reputable body shop with fiberglass experience. Windows need to weep away water which requires correct installation. Think about the alternative if you don't get the correct info here.
