Uh, when did you move to Anchorage?
Yep, just keep on washing and make sure you spray the undercarriage really good on a regular basis. Of course keeping a wax coat on helps the outside, but it's all the hidden parts where rust will start. Might be a good idea to remove your fender trim pieces and things like that every month or so and wash under there really good. Make sure you fix any scratches or dings right away too. As long as you have good paint coverage and keep it clean you shouldn't have any problem. Anyway, I would worry most about the undercarriage and keep it cleaned.
or, you could sell your Xterra and buy an Audi (double sided galvanized sheet metal) or a total POS that you don't care about!
So, is this a temporary thing or are you there for good?