My question is, if you were in my shoes what would you do? 

There is also fenced storage that could be rented out.

One of my tenants has asked if they could put a storage unit outside behind their space since they are out of space.

We also have an off-site 10 x 15 storage unit in a secure and gated storage facility. 

and 2) Which of the 3 options (or any other) would you consider if in my shoes?

I'd definitely give it a shot in your shoes, but since we're both newbies, that "advice" might not be worth much.

One of my tenants has asked if they could put a storage unit outside behind their space since they are out of space.

'We are not packing his stuff up and moving it to a storage unit. 

You can discover this by networking with active investors who engage in buy and hold (this can contain multifamily, office, retail, self storage, manufactured housing communities, single family, etc.), buy renovate and flip, note investing, hard money lending, WHATEVER. 

I have always rented my properties out during deployments, putting your stuff in a storage facility with BAH and rent rolling in is a smarter option.Step 3: when you return home, you can choose to move back into your property or buy that fixer upper you have been dreaming of depending on how much longer you have before your next PCS.