Subtank Nano is an excellent tank but sadly does not accept Kanger dual coils like it's brethren the big Subtank. I would second Rob's excellent suggestion but I've been having many issues with the Peakomizer with not only fitting coils but leaking as well. I had very high hopes for it. The Any Vape BDC Davide will take both Aspire BDC/BVC and Protank coils in it but not Kanger dual coil upgrades and is not a top filler. It's a very good tank and doesn't require a lot of customization of the base to enable the conversion between Aspire and Protank heads. You can find them cheap nowadays for around $17. I'll keep an eye out for a multi functional top filler Whiskey or perhaps a genie in a bottle to grant your wish.