The no-holes-in-roof concept is to minimize possible leaks. One drip in one hole once per day will rot out a ceiling. It is easy to prevent and seal the hole, yes, but also easy to miss one little crack. More holes = more potential.
On another note…
I trade campers almost every year, for the past 4 years I have had 4 campers. I do not get to see the long-term effects of my upgrades.
I have used both flexible (very thin, can be taped flat to roof), and aluminum glass framed panels.
The flexible ones are meant to be adhered flat to the roof and thus not intended to have airflow under. Has anyone had these for many years with no "over heating" or damage due to lack of air?
I had one flat panel go bad. Not sure if from a tree limb falling on it or what, I assume a connector inside became broken. $179 panel at the time (now $149 - expensive compared to glass, but for me worth a few extra bucks to be flat, aero and sleek.