Both the lower and the upper block wind of course, but the lower works specifically to improve airflow (drawing warm air towards the pot) and provide stability on difficult terrain. You can view the principle at minute 1:00 of this product video: http://vimeo.com/50641617
Yes the 27 Windshield Lower dose have a hole for installing a gas adapter
Yes the 27 Windshield Lower dose have a hole for installing a gas adapter