newshound laid this down on his screen :
The "proper" Renault glazed units are comparatively expensive but I reckon
all I need is one or two simple boat/caravan types fitted within the "single
skin" part at the top of the door/s.

Caravan and probably boat types are basically designed to have a
thicker panel to fit to. You would probably need to add a 25mm piece of
ply around the holes.

A better bet would be a car/van scrap yard and look for a van which has
had panel windows added, which can be reclaimed.