....publicly available at https://github.com/kvhnuke/etherwallet. You can download the ZIP there and run it locally.

This^^^^.  Do this^^^^.  Run their software locally on a computer that has a clean, new operating system (OS) load and has never been connected to the Internet.   Put the ZIP file on that computer via thumb drive.  Get TWO cheap, powerful ODROID C2s and use them as your (redundant) bank vaults.

http://www.hardkernel.com/main/products/prdt_info.php

http://ameridroid.com/products/odroid-c2