I agree with @BraceMaker about the clogged petcock issue. I ski all winter in central Texas and never fully winterize the boat. I just drain the block, exhaust manifolds and heater for the cold snaps. I pull the knock sensor out on the right side of the block and open the drain cock on the left....more often than not, the drain cock clogs with rust and scale and I have to pull it out too.
Another interesting thing to note: I rent a lift slip in a marina and noticed once last winter when I went out to work on the boat that about two thirds of the folks on my row (about 10 or 12) had wires running under their covers for heater or shop light. Enough people were on the circuit to trip the breaker so everyone that didn't drain was at risk. I was able to get the circuit reset for them before I left, but I know I won't rely on the power in that marina to save my block.