question is do you really even need anything? many tractors set outside all year round. just like cars and trucks.
primarily goal of any shelter, is to keep the direct sun UV rays off the rubber and plastic (including tires/hoses) to keep the stuff from breaking down quicker.
along with keeping the rain,snow,ice off the stuff. with 1 to 3 sides keeping the wind off.
con is, if not setup correctly, can bring in extra humidity, and/or extra heat.
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tarping stuff vs just letting it seat outside, can bring extra cons, such as mice and bugs that will love the nice warm and out of weather place you provide and eat up your wires and hoses.
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my vote is leave it outside naked, or car port.