I'm in the Canadian prairies, so we get real winters. I built an 8x12 shed where the floor joists rest on two pressure treated runners. I dug down into the dirt and made a trench for each runner about six inches deep and 16 inches wide and a bit longer than the length of the runners. Each trench was filled with crushed stone, then levelled, and the runners placed on top.

That was 15 years ago, and it's still going strong. Haven't had any problems with warping/heaving/sinking, but it's possible we're just lucky with ground consistency here.

You'd likely get better drainage by making a raised gravel bed with pressure-treated walls, but that wasn't necessary around here as the water table is low enough.