Usually a property offered at 3% CBB has a catch: busted properties, functional obsolescence, undesirable locations, or what have you. 

Personally, I think the West End becomes unaffordable, even undesirable, for a lot of first time home buyers and trade-uppers at ~$300k or $200/sf fully rehabbed.  

is it a desirable or undesirable place to live?  

Gerry,As someone stated, you might find a lower down payment, but you'll likely end up giving it right back again (or worse) in the form of higher interest, or some other undesirable terms.

If the higher risk is undesirable then you have to know you will do fewer or no deals

In other words, what are the best ways I can legally use to make the storage unit a profitable add-on rather than an undesirable burden?

I'm simply stating, in a red hot sellers market, the majority of the inventory will be undesirable and it's up to you to educate yourself and cherry pick based on your individual goals.  

In my ad for the rental, I set some guidelines that should help weed out some undesirable tenants.  

Prices in Fresno for all but the most undesirable neighborhoods are getting too high to cash flow for sfr's but there are still  smaller apartment complexes in B and C neighborhoods  that may work for you. 

However, there are a lot of undesirable areas here.