What do you think? Best outside car storage for this winter

Memike's suggestions are spot on. Building some sort of lean too over the car to shed rain/snow and cover with a breathable soft lined car cover would protect it the best otherwise don't cover it with a tarp. Tie it down securely so the wind won't beat your car to death with it. Gravel or cement will drain best. If over dirt or grass lay down a tarp 1st. Put it up on jack stands to save your tires and allow better airflow underneath. The rodents will have to jump higher to get in! This will allow you to start it up and put it in gear to spin, slowly, to help burn off moisture inside the motor and the engine compartment, keep the fluids circulated, your seals lubricated and the battery charged. If you can't start it regularly spray some light oil down the carb till it dies and disconnect the battery for storage. Coat battery terminals with grease to prevent corrosion either way. Wipe down chrome with a greasy cloth to slow down the rust. The home/hardware stores sell a desiccant that will suck up moisture in the interior and trunk and is more industrial than baking soda. You will need to monitor and replace this stuff regularly as it doesn't last forever. Some form of rodent repellent under the seats, trunk, glove box and maybe engine compartment. They love the top of motors as nesting sites. Don't forget to remove if starting. This is about all you can do except pray to keep the rust demons away.