I did the same for mine. I insulated the gloors, walls, and ceiling to be able to maintain climate. 12 plugs on 6 breakers in a 10X12 to keep from overloading. I used a normal 8,000 btu window hmr for cooling in the summer and an oil filled radiator style for winter heating. It is both my fishing and hunting/reloading room.
Oh yeah, to seal any cracks I used spray foam which after drying can be cut to install trim if wanted. I didn't want though