What size dehumidifier rod for a safe?

[spistols]

I have Liberty Franklin 27 safe. Should I go with a 12" or 18" dehumidifier rod? The safe is in a finished climate controlled walkout basement, but am on a river.

I left a message for @SafeCracka , and would like to see what others are using as well. Is bigger, better, with a dehumidifier rod?

 

[lexm41]

Install a 60 watt light bulb that stays on all the time and save money

 

[wirepuller]