Congrats on your smoker Chris! You can definitely program your smoker to drop to a 140 holding temperature after your meat has reached it's time or internal meat temp setting, but you absolutely must physically open the door and let the box temp drop. These smokers are so well insulated, that the temperature will not drop for several hours on its own, and your meat will become overcooked.
If you are opening the door anyway, I would just double wrap in foil and towels and rest in a cooler. It's a far superior way to rest in my opinion. You can rest brisket and butt as long as 6 hours in this arrangement. Ribs probably 4 hours or more. I did a test with a 9+ pound butt, and it took 6.5 hours for the internal temperature to get to 140 (foil, towels), and that was in a cheap Igloo Playmate cooler. So no need to "keep warm" unless you are going past 6 hours. If you need to keep warm in the smoker, then get the box temp down to 140-145, and add your meat back in. I'd wrap in cling film before the foil, to help keep the moisture in, if I needed to keep warm for more than 6 hours.
My smoker stays "outside", but with a cover, on a covered screen porch, completely protected from the sun, rain and snow, just not the cold. Even though I'm sure it can tolerate more weather, it seems too nice to leave outside all winter.