A loose, non-airtight stove is not very safe,, how do you control the fire if you can't control the air, at least reasonably well??
I'd highly recommend sealing up all the gaps and cracks and crevasses.. with furnace cement and rope gasket material.
You want to be able to control the fire to the extent that you can make the fire go out from lack of air..
Once you have the stove sealed up, you can use the under-fire air control to limit the air to the fire, and slow down the burn rate.. lengthening the time that the coal will burn between fresh loads of fuel.