I'm in N. central Montana so I get the same weather as you just a day sooner. I refuse to reload in the garage. Temp swings and humidity affect your scale as well, and in the winter it's just damned uncomfortable. I have to want to be at the bench, so if I'm cold bundled up I'm not comfy, heaters running (means air movement). In the summer it's just miserable in the garage so you open the door (more air movement).
I would advise a clearing out a closet if you have to, or building a takedown bench that you can set up in a spare room. In one house I had my entire setup in a closet, it was crowded to be sure but I made it work and it worked for 5 years and thousands of rounds.
Take a look here for some ideas
Woodworking Plans for Immediate Download from PlansNOW.com
Keep in mind the animals we shoot for food and display are not bullet proof. Contrary to popular belief, they bleed and die just like they did a hundred years ago. Being competent with a given rifle is far more important than impressive ballistics and poor shootability. High velocity misses never put a steak in the freezer.