I typically hunt Whitetails about 20 miles from Canada, in Northern MN. We've seen temps as low as -15 for days. Also seen major Winter storms go through, dropping a foot of snow. I've done this in less than suitable trailers but we've always had a good time and our socks are dry by morning. The most important thing is to have a good heating appliance and enough gas to run it. We typically bring two 100 lb tanks for a week of hunting. If it's warm, we may only use half of one cylinder. If it's very cold we may have to switch tanks during our stay.
I now have a trailer that is super insulated but haven't been Winter camping with it yet. I'm sure it will be more comfortable than the previous rig we used. Some things you can do to get comfortable--block off the glass,especially at night, with foam board. That stuff works great as a insulator and is easy to cut to friction fit window frames. Typically I use a duct tape flap so removal is easy. Skirt the trailer, again with foam board or wood sheathing. Straw is too bulky to carry and install unless installation is permanent. Still, I would want a barrier between trailer and straw. Think about your heating appliance. I pulled the RV furnace in mine and installed a different space heater that is more efficient and heats better than what was OEM. Look at the under belly and see how it can be better insulated. Most can be improved. A warm floor adds considerably to comfort.
Good luck hunting! A warm trailer is sure nice when the weather gets cold.
