Following,

I've been researching this very question for a week now.

So far, here is what I've gathered:

If you primarily spider rig, mount in on the trolling motor as you are primarily looking ahead almost all of the time.

If you shoot docks, cast to piles. or single pole off the side of the boat, mount it on a separate pole so you can turn it to the direction you want to see INDEPENDENT of the trolling motor which may be in spot lock mode and spinning all over the place.

I'm just getting started on my research so this is only what I've heard so far.

Another BIG question for me is:

Where do you mount the black box?

I'm leaning towards mounting it under the console near the fuse box on my RT188c, I don't think it has to be a dry location but I don't want to be stepping on cables or connections either.