Good luck! Everything I've done, including looking at them the wrong way, has managed to kill them. Tough trees to play with, or even stare at.
They're much hardier then people think. I believe they are rated as zone 7 trees, and I know they are planted in the landscape here around Atlanta, where it frosts and freezes from November through April. I have never grown serrisa as bonsai, but I suspect part of the problem with their perceived difficulty as bonsai is that they are probably babied, coddled, over watered, and over protected when they shouldn't be...just a guess though.
like the gravel topping