I've used the same procedure on I/O's for years. Drain all fuel, add stable to 3 gallons of fuel, put that fuel back in tank. Run engine to operating temp on muffs. Shut down, hook up five gallon pail with hose and valve, support above engine. Open valve, start engine, when down to half gallon left, fog carb intake till it dies. Shut down, remove all plugs/drain. Any liquid left is rv antifreeze. I can see refilling with antifreeze would be good, but empty won't freeze damage either. On the engine side, personally I would not be worried, but the manifolds maybe, both ways have their merits.