Thanks guys. I'm leaning toward the 4x4 skids with 2x4 joists 12"OC. I called the gas company and they said I absolutely couldn't build on the gas line. So a new issue is building it at a cost that I'm will to eat if they tell me to tear it down. Unfortunately I don't have room to actually move it if asked to since my garage extension goes right up to the easement.
Here's some pics showing the situation (the red line is where the shed would go):
