ensquire you are right to be concerned with one drain trust me many others will say if you can have two then go for it without you run the risk of a blocked drain doesn't matter if others say they run their tank with one I guarantee two is better and can even be quiter( check out herbie silent overflow) on reefcentral it's a great read on the risks of one drain and the bonuses of a true quiet system. There's always more than a snails that blocks overflows a large bubbletip can do damage as can fish or crabs urchins or snails that get trapped.
Sleep easy and go on vacation knowing you won't flood your display always play it safe as you can
cheers