Tony,
We had an extreme winter here last year and my girl wasn't inside. I was able to maintain a good temperature inside by just wrapping her good and tight with tarps. I was really surprised what heat I absorbed from the sun this way, even with snow on top. I had one small heater and a type of brooder bulb I use to keep my chickens warm. At freezing temps it would be 65 degrees by 9:00am. Under twenty and/or the wind blowing I didn't even try though. At 14 that certainly is a challenge when trying to spare expense. But being at 30 in the shop you should be able to get the inside cabin warm.
Stopping escaping heat will benefit mostly I think, and closing off the berth and access to other areas where your not working whereby minimizing the space.
Your right the tiki says it all.