Winterizing or in winterizing depends on the outdrive, I'm fairly well versed in the mercruiser drives, not so much on the OMC. Was thinking they had a unique fresh water system? Spend some time becoming familiar with the cooling system you have. Winterizing is basically removing the water or replacing it with RV antifreeze. The block and exhaust will have drain plugs. Check over the engine and drive lubrication. Consider a new fuel filter. Since it's new to you, I'd check everything, plugs, wires, battery, cap/rotor, etc. Good luck and congratulations on being a Glastron owner