Have you tried it? I’m always interested in trying different things to see what works better. Maybe the sun roof open a little will be enough depending on weather. Maybe with the windows cracked using the rain guards will make a big improvement.
Now without trying it I would think windows cracked with the sunroof cracked will let fresh air come in and then escape through the sunroof. I have a Maxair fan with a vent in the floor of the van. With the vent open up top with the fan off and my floor vent open I can still feel a draft as warmer air escapes through the vent pulling cooler or in from the floor.
Once spring gets here I doubt I’ll close either until the fall.