I have 2 false percula clownfish in a 20 gallon high tank with a catalina goby ad they're doing great. They have even paired up. I've had the larger one(female) for 4+mths.now and the smaller one(male) for 3+mths.now.
I'll be doing the same thing as FishTails soon. I've got a Twinspot Goby, and I soon plan on adding 2 Perculas. So, if I were you I would at least go with a 20G, that way you can think about adding a detritus sifter as well for the SB.