Hi UniFoxOS
I still think you are over complicating things. If you feel unhappy at just excavating and using hardcore to level the bottoms, the batter rail proposal is a simple and effective way of staying level. On small jobs such as yours a builder will just suck it and see. If you slightly over excavate it's not the end of the world. What is important is to ensure that the bottom of your excavation is solid. If you find soft spots you should excavate the soft spot down until you reach reasonable ground and then backfill. There is no need to remove adjacent solid ground to the bottom of a soft spot. The building inspector will want to inspect the bottom of the excavation to ensure that you have a solid bed. He will not be worried if the bottom is not perfectly level.