I think these vans are unique, especially the Gen 1 connects (2010-2013 in US, 2002-2012 if European) with the stamped recess in the metal, which matches the shape of the window if present. Enough digging in these forums can get you answers on things that aren't quite the subject of each thread - that's how I figured it out. I am working on adding glass to my slider doors which are even easier as it requires no cutting. The "panel" that exists in non-window slider doors (sliders, not back doors) is a fiberglass panel held in with a windshield urethane glue. I plan to remove the fiberglass with a thin wire glue cutter (like glass guys use) and then after cleaning up the residue, pop factory shaped window on with new glue.
If anyone here is interested, the NYC taxi version of the Gen 1 connects had a small sliding portion of the glass window in the sliding doors. They were not available on other models, and not available from the factory that made them (custom glass shop in Turkey I believe). Best way to find them is get on car-part.com and search for glass from wrecking yards.