Might not be room in the metro, but I did this in my s10 when it got cold out. I would take my hunting heater (propane) and fire that up. Nice and warm both air and radiant heat
One 16 oz bottle lasted me more than a month of using it to work in the mornings. I would run it for about 5 min before I was too hot then let the heat slowly die off till I got to work. Aimed at the window it melted the Ice very fast