Hi Kevin.
I spent 7 days at over 10,000 feet last September.  I am not really sure how the altitude affected the accuracy of my meter, but it seemed to work fine.  When I had a jacket on, I kept it in the inside pocket.  When my meter got too cold, I had to warm it up under my armpits for a while, then it seemed to work.  It helps if you have a fast meter, too.  I have a one-touch ultra II and it was lightweight and worked pretty slick.
I did seem to have higher sugars, especially at our camp at 11,000 feet -  despite all the exercise.  Also, the temp dropped below freezing for 3 or 4 nights - it even snowed on us.  I kept my insulin in a frio pouch and tucked it underneath my sleeping mat at night to keep it from freezing.  I love the frio pouches - they work particularly well when backpacking in warm weather, too.  The only drawback is that they stay damp, so you need to be able to store it somewhere where it won't make clothing, etc. damp.  There have got to be other sorts of insulated pouches for carrying insulin that are more suitable for cold weather activities.  I also made sure all parts of my pump, tubing, etc. were close to my body when the temperature dropped.
Cat

Hi Kevin.
 
Great questions.  Which reminds me that I better get finished with helping DESA with a FAQ on this very topic!
On Rainier, as you already know, you'll be dealing with some warmish conditions on the appraoch and colder temps higher up.  Your meter will be mostly be affected more by the cold temperatures than the altitude.  I can pretty much personally vouch for most meters on the market if kept warm enough and your max height is top of Rainier.  Insulin needs to be protected from excessive heat and freezing temps.  Pump, tubing needs to be kept under your clothes in a protected place close to your core body heat.
 
Many ways to accomplish this.  Figure out a bag which will hold your meter close to your body and doesn't require you to remove the meter from the bag.  I think that i may have a picture of my own example somewhere on this site. 
 
How blood sugars react is tough to summarize.  It depends like everything.  Highly aerobic activity at any elevation will make you insulin sensitive.  My guess is that when type 1s are unacclimatized and going to higher altitudes, they could see a relative increase in insulin needs.  All very individual, but I would suggest spending as much time at higher altitudes and seeing how your body adjusts to the new variables.  I recommend against taking acetazolamide to offset AMS symptoms..   
Rainier is a beautiful place.  I'd love to return and do Liberty Ridge.  Some day.
 
ciao, dp