RE: Avastar fuel tank
I also have an Avistar awesome little airframe. I put in an OS 46ax and discover that the stock fuel tank only provides barely 10 minutes flight time.
I am going to try to fit a Sullivan 12 Oz flex tank. I have looked through tower hobbies, and a few other mail order type sites, and haven't found a better fit yet.
The flex tank is just barely oversized in one dimension, but longer than the stock. being flexible, (I squeezed one) it should definitely fit. When it arrives, I will
use a razor saw or knife to cut away some of the inner parts of the former ribs so I can addd the tank PLUS a bit of latex foam.
I hope this helps. :-)