Securing underhouse area for storage. Looking for advice

Our house is raised on stumps. At the front it is about 1.7m off the ground. At the back about 2.5m.

The whole underneath the house is concreted however it looks like 100 different little slabs so there are lots of cracks in the slabs. We want to use the area under the house for storage and I'm at a bit of a loss as to how we go about it.

Option 1: Fence it in. We would basically just fence off the area under the house. We would also create a small lockup area within the fenced off area as an added level of security for the more expensive things (eg. power tools, etc)
Pros:

• Improved airflow under the house (at the moment it is all open under the house so we get a nice breeze going through there in summer. Our house is small yet in summer it stays relatively cool even without ceiling insulation, we attribute part of this due to being raised up off the ground and getting the airflow underneath).
• Cheapest option
• In my opinion the nicest looking option from the outside

Cons:

• Not private (eg. people can see under the house)
• Rain could come through the fence slats (not much rain would get in but it does limit us on what we can put up close to the fence slats when storing things)
• Being open air there is nothing to stop noise coming up through the floorboards into the house and vice versa.

Option 2: Build blueboard walls with some windows in them.
Pros:

• People can't see under the house easily
• Rain won't get in, better sound deadening (won't get as much noise coming in/out through the floorboards).

Cons:

• More costly
• May not look as nice
• Problems with moisture as with all the cracks in the slab we get rising damp.
• More likely to attract vermin / bugs being dark and quiet (we have one part bricked in at the moment and it is always full of mouse droppings and full of mosquitos even through I regularly spray there. Our area is close to a creek and in the summer months we literally have big swarms of moquitos).

Option 3: Same as option 2 however we lay down a waterproof membrane over the existing slab and then put another slab on top.
Pros:

• Hopefully no more moisture issues
• Increases uses for storage (eg. We could store clothing and such in boxes down there).

Cons:

• Most expensive
• Loose some height due to the new slab
• Other cons same as Option 2

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