Hi Charles,
I have the Cole Hersey parts as well and am considering installing it for battery top off - though I'd have it inside my baggage compartment.
I've studied the "GroundPower" article quite a bit to understand the instructions for installing the threaded toilet seat bolt. I think I understand it - basically:
1) reduce the size of the flat heat until it just fits in the back end of the receptacle.
2) Grind down most of the back end of the receptacle
3) Push the bolt head into what's left and fill it with solder.
I spent a lot of time looking about for how the unit is supposed to be installed as is - without modification. Can't find anything.
I'm also considering these:
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
They would be lighter, flatter, not require any modification and the holes you see in the middle of them go all the way through so you could use those to mount one of them. Though again I'm installing this in the baggage compartment.
Let us know what you decided upon and how you're going to do it. This is a common project and the more ideas and solutions that are out there the better.