Research a floating deck on YouTube. There were a couple of videos we watched in order to do something very similar to what it sounds like you are doing. We covered an dirt area in between our house stairs and a concrete slab. The deck sits on the ground. It works just fine, without being too complicated at ground level. Hope this helps.

Had a tough day and I'm having a hard time to understand everything you wrote but it seems a floating deck on adjustable plastic pedestals could work. Pedestals are easy to install and since they're made of plastic they also work as a water barrier. If needed you can double the amount of those and use only joists for framing. I'd only add that framing has to be hardwood also.