ideas/recommendations to make underdeck space usefull

Hi all. I have a raised deck with a land slop of approx 12% under it. I'd like to make that usable space (more for storage than anything else) 25x15ft approx.



it starts at about 7 ft high (existing patio) to 4ft at top of slope over the course of 25f. I've started to dig it out, and my current plan is to make it 7 foot clearance throughout with proper pitch from house and put on fabric with gravel over it. The problem then becomes with preventing erosion.
Original plan was to do a retaining wall block wall, but that's a lot of work and expense for just storage space.
Before doing that, I was wondering what suggestions, if any, you all have. There's probable other options that would work just as well for the function, that I just haven't thought of, so suggestions are welcome.

 

Look for a deck ceiling system that will catch the rain water and divert to the outer perimeter.

 

I used corrugated fiberglass panels to form "roofs" under a 2 level deck.


Fiberglass panels between joists of upper deck to shield lower deck.

Separate "roof" system below lower deck over wood pile. (Panels on top not visible.)

"Roof" structure over wood pile is separate from deck structure. (Panels not visible.)