I don't know about the amps for your situation. I'll let you and
others think that one through.

One thing though. The picture in your link shows the wiring panel
coming off the #2 part of the switch. I prefer to have my wiring
panel come off the COMMON (not common-ground, but common-
positive) part of the switch. That way I can decide which battery I
want to be using for my panel.

Another thing. Some A/B/ALL switches have a "make before
break" connection. That means that as you switch from, say,
battery A to battery B - that battery B will be connected to the
circuit BEFORE the connection to battery A is broken. This
prevents a condition where NO battery is connected for a
second. This prevents damage to your altenator. It costs a few
bucks more, but I think it's a good idea.

Gary