I've look over the input I've gotten from several folks who answered my
question about how to set up a second battery. Here's what I know and
what I don't know:

The ideal place seems under the drivers seat. Since mine is a Westy,
there's already a silver relay under there with a part number ending in
9813, 12 v 30 a.

What does this do?

Into that relay, coming from the front of the car, is a blue wire, a
red wire and a red/black wire.

Out of that relay, heading to the fuse terminal and going back to the
camper stuff, are two larger red wires.

I've looked at the Bus Depot wiring diagram long enough to know that if
I know which of the two red wires to put on terminal 87 of the new
relay, and where to conveniently grab a wire that's only hot when the
motor is running (or the car is switched on is OK with me) then I can
complete this task.

Thanks,

Jim