Can confirm, this is indeed the case. The thinking at the time was that the water would simply drain out the drain holes in the bottom of the quarter, not realizing how easily and quickly they would get clogged. Or maybe they did, as there are several mentions about maintaining and keeping these drain holes clean and clear of dirt and debris throughout the life of the vehicle in the FSM. And not just on AstroRoof optioned vehicles either, but ALL G bodies.
Still, not The General’s wisest decision.
