Onion in Cold Storage

Dear Members,

I have cultivated onion in 2 acres land.
Can you please advice me up to how many days/ month I can keep onion at cold storage?
What is the maximum temperature and humidity required to make it safe for long?
Is there any method I can apply if I want to keep safe in house (without cold storage)  for 6 month or long?

Regards,
Siddhartha.