Larger box spaces tend to take longer to lease out as bigger companies are slower to move and rent is typically higher compared to a larger pool of smaller tenants going for the regular type spaces.National tenants tend to want brand new buildings with higher ceilings for storage and shipping.

We have also done as much creative storage as possible.  

It's an unfinished basement that is used for storage, laundry, and HVAC.

Or are there other ways (parking, laundry, storage) etc... but key is to leave some meat on the bone for future investors.

If you are an Accredited Investor, you could place that 100K with an experienced sponsor in a real estate syndication in any number of asset classes (Large Multifamily, Self Storage, Mobile Home Parks, Assisted Living Facilities).

The goal is to pile up enough cash to buy large value-add multi-family, storage units, mobile home parks, not exactly sure yet. 

I don't give a frog's fat butt if it makes his job more difficult, and honestly, you have to do math anyway during the course of the loan.

Diversify portfolio with investment in Self-Storage facilities.

My point being it is a difficult environment for everyone (except sellers), and to illustrate, a syndicator I have been following (wellings capitol) has given up on multifamily for now and switched to self storage after a history of insisting they would not do self storage!

Since this is a SFH, you're not going to force the appreciation by adding storage space.If this is a long term hold, you'll recoup your investment no problem.However, if you'll looking for yield, then I think your new dollars may be better spent elsewhere.