Does anyone of you have some experience with snowboarding or skiing with a DSLR camera on your back? If so, can you recommend me a good backpack?

I would love to take my camera with me on ski-trips but I want it to be as safe as possible... I would not attempt tricks or anything when I have the camera with me, but I want it to be safe just in case I would fall or anything...

Anyhow, it must also be easy to take it out to shoot some pictures and then put it quickly back in there without exposing it to too much snow or water...

thnx