They sell a box stove at Harbor Freight for around $160 bucks. You can cook on it, and in a small shed it would drive you out in no time. I have a friend with a cabin that put one of them in and he can't fire it hot or he's in that cabin with the doors and windows open. Wood is easy to get if you have state or federal land around and a willingness to work. Some counties allow you to take out trees they cut along the sides of roads.

I was going to get one of them heaters Breechplug was talking about and heard the same thing.. they suck heat. Even one of them little heater buddies throws nice heat. And if you're casting, you have the heater off that too. I am sure you will be fine.