No my Beast dosen't leak at all with the pre-built coils, though I'm using max VG which might help that. Also I leave the airflow open when I fill from the top. Some tanks have airflows that seal well others don't. If they don't seal well then it makes little difference closed or not. Haven't yet tried the RBA in it.
Hi Mongo
Just a small change to what you said. Tanks don't build up "huge vacuums" while vaping. They have very small vacuums created by the weight of the liquid in the tank. The reduction of air pressure in the top of the tank is equal to the weight of the liquid thus preventing the liquid from flowing. When you break the top seal then as you said the change in air pressure allows the liquid to flow.