Boy you are going to be beat up on this one! :B
My suggestion would to replace the roof vent over the cabover, if it has one, with a
Skylight this will let the light in and can be covered if necessary. Some newer Class Cs have them.
I would think it would be easier to seal up than a front facing window that is subjected to strong wind and rain while driving.
There is a saying that you will hear pretty soon and often here,"windows in the front either have leaked, are leaking, or will leak." seems to be the only help some members can come up with which is no help at all.
Good Luck!
