What length is your Flying Cloud going to be? I just took delivery of a 2023 27' FBQ and the "nerve center" appears to be under the curb side nightstand. There is a small access door from within the outside storage, but otherwise it is pretty inaccessible without removing things.
I too was wanting to get into that nest of wires to add in a smartshunt and after some quick eyeballing it appears to require some thought on getting access. My Caravel
that we just traded in had a nice big access door so it was easy to see and work on everything.
I haven't quite figured out how to remove the nightstand to get a good working space, but the weather hasn't been great here so just haven't put a lot of time into it yet.
My guess is you'll have to place those batteries in the outside storage compartment or use up space under the queen bed.