Hi folks. I've currently got the Kanger Subtank Mini, Subtank Plus, and Aspire Nautilus. I'm using these with an IPV D2 and a Sigelei Mini. I find that I go through coils faster than I would really like to. I'm wondering if there are more efficient tanks out there in terms of having to not buy coils every 3-4 days? Also, the Kanger coils seem to be VERY hit or miss. Lots of duds out of the box. Opinions and info welcome. Thank you.