Our Natural Green Laredo X sits outside too.
In the winter on my vehicles I use Collinite 476:
Just did the Lexus this weekend, the Jeep is next. I used to detail cars professionally, and am an avid enthusiast now. I've used just about anything, personally I have never found a sealant I liked, including the Ultima product. I think a good Carnuaba may not last as long, but the look and protection can't be beat. I've had problems with water spotting using polymers (about the worst was with the Ultima Paint Guard actually). The Collinite wax is a VERY heavy carnuaba (kind of a pain to use too, best to apply per panel and immediately remove) and will get you through the winter. In the spring I always start using stuff that has a little better look, but the Collinite can't be beat for protection.
I think when a vehicle sits outside, the biggest thing you can do to keep it nice is wash it regularly.