You can already buy a 32gb SD HC card or a 16 gb Memory Stick (soon to go 32gb as well) , so given that the compression issues have been largely resolved with AVCHD anyway , I have already declared DVD and Hard Drive dead formats (at least for backpackers)
Extra batteries. Yes...
Some batteries will record for about 3 hours and remain charged almost fully for a couple of months. There are several very compact generic batt chargers, so get a couple of adaptors (the European and American version are the most used) and you should be in business. Otherwise you can try something like the Solio
To be realistic, no one but yourself will want to watch more than 30 min, max 1 hour of your "exotic" trip. So in most cases if you are careful , three or four hours of footage could be edited down to 30 min of watchable material.
But just like joining Amway, if you need to get rid of some "friends" show them very bit of your movie.....
Another interesting camera is the Canon HF 10, pretty much the HG30 solid state (SD HC) rather than Mini DV.
As far as low temps and condensation, again I see solid state as the way to go. Tape can stick, DVD can suffer (dew warning...) and Hard Drive is a bit hit and miss over 3000m." Working for some" is not my favorite option.