Considering your practicing for winter hunts it makes sense to me to practice in the same cold elements you plan to hunt.
If your practicing indoors with a t-shirt on then when the moment of truth arrives and you have 3 sweaters and a jacket, a hat and a pair of heavy gloves on. You wont be familiar with the feel of pulling your bow back wearing gloves and heavy clothing. Your best bet is to practice shooting as you would be hunting.
My opinion!