What Owen said. And I totally banged in a new motor which came with a proper mount, the stock mount just isn't a good system.
My servo is inside, siliconed to the wall and with a rubber boot (bicycle brake) at the exit. The ESC gets a bit hot but this thing sometimes gets a beating, so for mine it's best inside too.
I got it as a seaplane rescue boat, but so far it's only ever been the other way around... I think it needs something on the front to grab onto things. Oh, and make sure your ESC has reverse!