A gargae ? Great ! Just insulate the box on the garage side.. The open end would be open to the inside of the viewing room, so it would stay the same temp as the rest of the house.. And yes, just frame it to match the rooms moulding.. Power would probably be accessed from the garage, and the other cables could be routed up thru the attic, then into the garage side of the box.. Invisable ! Sweeeeet..

LFE ! The rest is just details..