How to harden and seal soil under my floor without using concrete or paving.?

Hi If I dug out a bit under my Living Room floor, I would have quite good storage space. I would not dig below the level of the footings to avoid underpinning. It would not be headheight but still would be a usable space. There is a floor hatch already. I need to do something about the soil though. Pouring a... show more Hi
If I dug out a bit under my Living Room floor, I would have quite good storage space. I would not dig below the level of the footings to avoid underpinning. It would not be headheight but still would be a usable space. There is a floor hatch already. I need to do something about the soil though. Pouring a concrete slab technically requires permission from my council and is expensive. Paving will be difficult due to the lack of head height. I have used plastic sheeting before but it breaks down and tears.

Does anyone have any ideas for how to harden and seal soil already in place so it forms a reasonably smooth and hard surface. I am hoping there is some sort of penetrating and sealing liquid that I can pour over the soil once I have smoothed it out and compacted it as best I can given the low head height.

Does anyone have any ideas? I read about suggestions about bentonite?

Thanks
Update: PS I would like to seal the soil as it will also help keep out cockcroaches etc. I could lay down vinyl or similar but am concerned that it will be loose at the edge as I cannot glue it down.
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