Our 2002 Sunline had a front window that opened (jalousie style) and it never gave us any problems. I would look for a crank out type window....not a slider as I think it would be less prone to any type of water leak. I wish our Minnie had a front window as they really help with ventilation. Instead, I'm going to be installing a Maxx Air vent system.
A quick Google search for RV windows will bring up several companies that sell windows and give pretty good directions on how to measure windows.
Easy RV windowsHehr windows and others
2012 Newmar Bay Star 3302
Blue Ox Avail
BrakeBuddy Advantage
2015 Malibu
"Get busy living, or get busy dying."
Andy Dufresne, The Shawshank Redemption