In reply to JohnV:
Depends on what you're doing and for how long, but even trekking there can get pretty wild, weather-wise. I did the W trek in the Paine, before a climbing expedition, and it rained for two days. One night, at the 2nd-last campsite, in the forest, it rained so much the whole area ran with water an inch or two deep. Our Bibler Tempest (on a relatively well-chosen site) started to float, anchored by pegs! but most of the trekkers had cheap tents and just got flooded, mucking up their entire day and trip, whereas we just got up early and moved on.