I will not install the 1 1/2 Styrofoam and try to seal the floor system as JJ recommended. BC had some concerns about return air. The room does have return air vents and was actually professionally installed. The HVAC installer and I were talking after he roughed my house. He made a joke about the air from the heating ducts being "cold" by the time it got to the far bedroom over the garage. Then after my neighbor said his room over his garage was cold all the time I started to worry. Maybe he just doesn't have it balanced correctly. Since I have a gas run to the garage, I will have the heated garage option just in case.