If you want a tank like that (bottom coil and air) to leak then lying it on it`s side is a good way of going about it. When not in use it`s best to turn it upside down. Tanks that are top-fill but have no liquid control are almost certain to leak or gurgle because when you remove the top-cap to fill it you have removed the seal which prevents gravity acting on the contents so the liquid will flow through the wick ( because wicks be wickin`). Closing the airflow when filling will do nothing to prevent leaks. If you think otherwise, then please provide an explanation.
To reduce the possibility of flooding when filling then do it really quickly and get the top back on ASAP