I have an auto-change over and have always kept both tanks open while camping.
I believe with the auto-change over regulator, it only feeds off the assigned tank until it's empty, then the regulator transfers to the other tank and indicates the assigned tank is empty. If this is not correct, please someone correct me.
I monitor the tanks regularly, when I turn them on before a camping trip, during a camping trip, and when I turn the tanks off after a trip. When I see that the assigned tank is empty, I switch the regulator lever, remove the empty tank, and fill it, with no interrupt to gas flow to the camper.
Hope everyone has a fun and safe Memorial Day week-end.
Hutch