I just did an experiment. I needed to brave the snow and ice to get to home depot yesterday because my digitial thermostat in my home started to die. It's not good when it is 24-25 degrees outside and thermostat gets an attitude.
While at HD, I as 250W Halogen work light for $5. Hmmmm...
I took it home, managed to chip the ice off the airstream and plug in the light and turn on "low" the el cheapo 18" box fan I used to circulate air when running the dehumidifier. The light is centered side-to-side about 4 feet form the front wall of AS with the fan about a foot closer to the front (or 3 feet from the front wall). the remote temp sensor is located on the counter top just forward of the closet on the street side 1 foot from the window (for the best radio transmission).
Now the data: The temp at my house has been pretty stable at between 24.5 and 25.2 for the last 24 hours. I have had a remote temp sensor in the AS for the last month and it has been tracking outside temp within a degree or so provided that the daily variation is below 5 degrees.
When I added the light at 6:45PM and turned on the fan, the internal AS temp was 25.2F degrees and the exterior temp was 24.6F. After 12 hours the exterior temp is 24.8F and the internal temp is now 30.4F. Basically, I'm getting about a 5 degree increase with the 250W Halogen work light in pretty darn cold temps for PDX.
Your mileage may vary, but I'm happy with the result. With more typical PDX temps... this light would probably keep the trailer above freezing.