I have a 10x10 Flex Bow. The 10x10 is a good size for two people in cots, but I don't know about running a heater in it. If you don't mind the extra weight and the challenge of finding a big enough tent site, you might as well go bigger.
The benefits of the Kodiak Canvas are vertical walls, the feeling of quality, good performance in wind. The drawbacks are weight, packed size, and poor handling of moisture (in my opinion)
The poor handling of moisture is probably just part of having a canvas tent, and I probably need to waterproof the thing with silicone spray. But the tent has a big nearly-flat top - when it unexpectedly snowed on us on an August trip to the mountains, the snow stayed put up top on, and the tent leaked. Also, I have been unable to find a setup for the awning that keeps water from pooling on it. It's a shame, because without the awning it's impossible to enter the tent in the rain without water getting in the tent.
The tent takes forever to dry and becomes a big mess if you have to put it away wet. Unlike a nylon or polyester tent, it's difficult to hang it up in the garage to dry out (depending on your garage, I guess).
If I could do it over again, I'd buy a quality tent that was lighter but could handle rough weather. Unfortunately this would mean sacrificing so much of what is so nice about the Kodiak, because the Flex-Bow is the only design of tent I've found that is so roomy but also seems weather-worthy.