I want to add an addition to my camp on an inland lake in Gwinn, Mi. The soil is all sand. My question is what kind of support do I need under the slab I plan to pour for the floor. I was hoping that just putting down some concrete tubes about 4 feet would be enough support.

I think there's a story or two in the Bible about folks who build on sand. If you can't get down to a flat site of solid earth or rock to pour a slab you will need to excavate a complete footing. I think the frost line in your area is 48"+.