All grounds go back to the battery - no airframe grounds are used. As far as protection is concerned - there are custom made fiberglass "hats" that cover/protect all connections on the terminal blocks. Water/moisture proof - no, but pretty hard to figure how that might be an issue from operating where I live (desert). And re/different connectors - this install was done almost 30 years ago, before the advent of all the certified connectors filtering down to our level. That being said, I probably will do the same thing on my -3 when it's time. Pretty easy to make/break the connections as needed, and no special tooling required.
YMMV - Old school, but it works.
HFS