We did this last year when we went to camp in Manning Park, not so smart as we didn't think about it until we got up there but there was still snow on the ground up the highway but it proved to be an exciting and interesting trip. It poured for the 5 hour ride to camp but stopped for the 45 mins it took us to setup our camp. We stayed dry due to the ST's awesome weather protection and our gear and stayed more than warm enough on the trip up due to our Gerbing Heated Gear. It was colder and wetter at camp than on the bike in the rain there.
Our Ride: 2003 ST, with standard saddlebags and Pan Rear trunk. We had not external racks or things packed on top of the bike. As we were going to a Wedding (Camping Wedding, it was awesome) we did not bring a stove (but brought everything else required for camping.)
We fit everything that we needed, and had a blast. The biggest problem that we had was not with space but keeping the bike below the maximum weight limit. We maxed out everything (bags, trunk, etc...) as per the manufacturers maximum weight capacities and set off with some space left over.
The bike itself handled very well for the weight it was carrying, but it did handle like a ripe old pig compared to how it normally handles. Then again, we normally don't set any speed records (especially 2-up.)
If we were to do it again I would invest in better back-packing gear. The gear that I have is already relatively compact (smaller than anyone normally uses car camping) and is back-packable (I've done bicycle camping trips with it.) I would invest in lighter (smaller) more efficient gear. Mainly a lighter tent, stove and sleeping bags.