Concrete bunker smell proof?

Hi,
My old house had a dettatched garage with a mechanics dug-out in it. It measured roughly 12'x4'x5'. I grew Dirty Harry all through the winter. It was -25 outside but warm inside. Run a small heater during lights out and raise the conatiners up and keep the roots warm. Ran no-filter, as smell wan't an issue but the frost build up was hard to eliminate on the outside window.

An ozone generator in the garage would be a good plan. Even if he doesn't need it to keep smell down it will kill the smell from opening and closing the door.The garage is not a room you spend a lot of time in so i'd be comfortable with using ozone in the garage if it were me.