That would work. I prefer to do it the other way, though; manually making things detail.
These shortcuts are very useful:
Control + d: Show/Hide detail brushes
Control + m: Make a brush detail
Control + Shift + s: Make a brush structural
I usually turn off detail brushes with Control + d, then fly across the map, selecting brushes and making them detail with Control + m. If I accidentally mark a brush that blocks the void as detail, I either undo or quickly unhide detail, select the offender, and make it structural again. For me, somehow, the second is faster.
Another thing many mappers do is to design blocky rooms made out of caulk and making almost *everything* detail. This works fairly well too.