I'm going to place the shunt and ANL adapter next to the battery contactor on the left firewall. What is best practice hardware to use, and is a doubler necessary?
In both planes that I've built, I did not put a backer plate in. I've never had a any problems. Most would say a backer plate is a "best practice" though. As far as hardware, I used stainless steel screws and lock-nuts (1/4 inch if I recall), 1-1/2" long. The counter sink in most ANL fuseholder is 82 degrees. If you end up going with a backer plate you can use nutplates instead of lock-nuts, just make sure the the screws are fine thread (1/4-28). A link below to an example of screws that should work: