Same thing here, SteveT ! My first overnight campout at LCG, my 5x8 tear only has 1/4" walls to help with weight, so I used 3/4" foam board insulation in the walls and 3/4" plus 1/2" in the ceiling to fill space .
It was pretty chilly at midnight, crawled in and tapped open the ceiling vent but was cozy under just a flannel sheet and one blankey !!!
HAPPY !!! and stayed plenty warm. Also , never heard any cars, etc.
Julie