I've had a clown pleco for years. Until recently I kept him in a 20 gallon tank. I moved him to a 33 so I could house some more fish with him, but he was doing just fine in the 20. I don't understand why folks are saying that you need 30 gallons for a clown pleco but only 20 for the Bristlenose or Bulldog, when the bulldog needs cooler water (hence more dissolved oxygen), and the Bristlenoses get bigger than the clowns and poop every bit as much (at least the common Ancistrus cf. cirrhosus.).
So, bottom line, that should be just fine.