CanoeingHarry: "There was an island I stayed on a few years ago on Burntside but if I remember it was difficult because a fallen pine. It was marked as a site but can't find anything online. How can you find winter sites?"
In Winter camping of the BWCA the Forest Service allows you stay at locations that are not designated campsites to lesson the impact on campsites. You can find a spot in the woods that is not so wind whipped like a lot of canoe campsites. Some people stay at or near sites because of the fire grate and bathroom. I will let others more familiar with Burntside to address your other question.