Well, as far as protection for a rider stored outdoors:
Don't "Wrap it" in plastic or anything else that will seal in moisture.
The best protection would be to cover the machine with rigid material of your choice. Some ideas could include a hard plastic kiddie wading pool turned upside down, a fiberglass roofing panel, even a sacrificial piece of plywood.
The idea is to shed water/snow while leaving the sides open to ventilate.
Wrapping up a machine in poly sheet or a plastic tarp can be as bad as (or worse than) leaving the machine outdoors with nothing over it.
The cover needs to be rigid so water has no low spots to collect water, which will eventually break through and flood the machine underneath.

Thanks for the timely reply. I will pass it on. My experience with folks who park cars outside on grass for a long time is that moisture from the ground comes up underneath. I have seen chassis and brakes completely rusted to the point of being frozen in place. Also the tires sink into the ground over time. I will also suggest we place a vapor barrier under the mower.

Hello; I mowed with the machine yesterday and it is running much better. The exaust is no longer black and does not have the overrich smell. Has a clicking in the valve train, I do not have enough experience with these engines to know if they have soild lifters. If so, that can be adjusted out. The owner got the machine from a relative who had given up on it. He is considering adding foam to the rear tires. Both rear tires are leaking air thru cracks in the sidewall from age. does anyone have experience with tire foam. I also recommended 30 weight detergent oil to him.