I would advise against the Trek 820 (Not that I have anythign against Trek - I ride a Trek when it snows...
) I had a Trek 820 and as soon as I started pushing it hard the rear dropouts bent and beceame misaligned. I am afraid that the steel used in the frame won't take the rigours of serious touring. Especially off road touring.
This is, of course, based only on my personal experience. The Trek 820 is a fine commuter/entry level mtb, but I wouldn't trust it as a tourer.
Magnus Thor
Iceland