The vents in the closet, will it be vented to the bath or the main cabin? The main purpose of venting the closet? Is it to warm it up in there? To change the air is a commendable goal, just have never heard any one say that to vent that space would be nice. Is it thought to accomplish this, with one high and one low, by using the thermo siphon principle? Or to take advantage of the forced air from the bathroom heat duct?
I would love to see a small waste basket installed half in/half out of the closet door. That would make it accessible from both inside and outside. Maybe the vent could be combined with this goal?