In my previous double duty rigs, I've always had a rear locker. Though the rigs were 4-6k#'s and this is 2-3 times as heavy as a Trackick. I'd say that if you haven't driven your vehicle on ice, yet, don't get a locker. Get experience under your belt with the vehicle and the driving with the tires. You'll notice quite a bit of difference. Then in the spring, when it's all thaw, get your locker put in. Hopefully, you have some experience with the vehicle off road, and adding a locker then will help you learn about it's capabilities off road. Then when winter comes back around, you'll have some time and experience.
Why is everyone seemingly wanting to jump right in? Take some time and get to know your vehicle. Jumping right up into the saddle is not the way to go.