10kWh is enough to run one 110VAC outlet at full capacity for about 10 hours. I don’t know where that 10kWh figure comes from but most American houses use between 15-30kWh per day.
So that 10 foot cube would need to be closer to 15ft cubed. It’s huge. Perhaps the foundation of the structure would work, as someone else mentioned.
Next time, print forms and create a mold. You’ll spend a whole hell of a lot less money and you can make it food safe by applying wood putty and sanding the forms.
I might do that myself now…