If there is no existing lien on the property, then there is probably someone who would be willing to do it now.

@David Key It means residential owner financing is subject to the SAFE Act and the Dodd Frank law which impose significant regulation, expense and risk on owner financing. 

Obviously you'll have some costs associated with the HELOC, and you want to be very sure you can sell your existing house quickly (if cash on hand is tight). 

Now a secret storage space a few inches deep the entire width of a wall can certainly exist unknown.

Was your question based on having an existing tenant?  

Two bedroom four car garage layouts don’t exist, so a unique property like this is the only way I see to have everything under one roof without an hour long commute.

Like the roof, A/C, type of electrical wiring, water heaters, garage existence and attached or detached, fencing, windows,  flooring type throughout, concrete slab or pier and beam foundation. 

It's an old row/townhouse in B class neighborhood and it has duct for heating system so I have an option to add central A/C to existing heating system.

Find out if you can just add more insulation over the top of the existing insulation or if somethings wrong with the existing insulation.  

The existing tenants would not pass my criteria of 3x the monthly rent , 600 credit score, no evictions / credit history since they do not have any credit history / credit cards etc.