Protecting your tractor is indeed smart.
I use two containers.
One on the left side & one on the right.
Built a roof over the open span. Very simple & it works.
Sure the ends are open but it stays in Florida. We could always use that thick ''see through'' hanging plastic but our tractor is just short of 20 ft long when the back hoe is locked to one side. It is out of the wet part of weather there.
Keep in mind there are 20 ft length & 40 ft nearly all steel shipping containers.
Some have barn doors on both ends.
Usually there are only one set of barn doors on one end.
The refrigerator units have the barn doors on one end & a removable compressor w/ its fans etc on the other end.
I have seen these as drive through shelters for other equipment, such as lawn service equipment.
These containers are also made of a lot of stainless steel & aluminum so there is usually less rusting.
Would suggest, to reduce the floor from rusting out (very common when set on the bear ground for long periods of time), use cinder blocks to elevate the container to better permit dry air circulation.