Will my 20ft pontoon boat be ok in a wet slip at the lake all winter?

I live in Texas, and the slip my boat is in is on Lake Tawakoni. I plan on changing my lower unit oil and grease, and more than likely getting a tune up done. If it will be fine in the water over the winter should I trim the motor all the way up or down? I have a 50 hp Nissan outboard motor.Will my 20ft pontoon boat be ok in a wet slip at the lake all winter?
If the lake never freezes you shouldn't have a problem. If the lake freezes you could still leave the boat in, but you'd need a bubbler system that will prevent the ice from crushing the hull. As far as storing the engine you want to store it in the down position if your counting on the hydraulics to hold it up out of the water. Using the hydraulics all winter is likely to damage the seals around the piston, and could cause premature failure. This is true on a trailer as well. If you can find a way of raising the engine and then using a wooden block or a pin on the engine to support the weight of the engine. You could then remove the pressure from the hydraulic system and store the engine in the up position just fine. You just might want to apply a little extra grease to the exposed section of the piston that's left exposed.