Check the county ordinance to find out what their definition of "enclosed" means. It should either be published on line or if not you'll have to go down to the courthouse. Unfortunately you're going to have to get them inside and out of sight to keep the busybodies satisfied. (or register them all, but that would get real expensive).
If it's not defined, then tarps around the buildings may get you by for a while or at least give you a point of argument in front of the judge anyway. You would want to hard cover them eventually to protect them from hail, etc. Cheap metal sheathing should work for most of the buildings in your pictures.
As long as they're out of sight I would think you would be fine.
I would assume that buying a license as a salvage yard (or you can call it a vehicle rescue facility if the term salvage yard hurts too much

) and putting up a fence to meet those requirements would not be possible in your zoning area? It may be worth checking on as there is no way a salvage yard could have all of their vehicles under cover.
edit: Whatever you can't get under cover right away, you may have to rent some of those storage spaces at a local storage facility. At least until you can get covered storage put up on your place or get some of them sold so they don't go to the crusher. Sadly it's going to cost you a bit to fix this and ignoring the problem is not possible. If it isn't fixed not only will they fine the p*** out of you, but the county will eventually come in and haul them off to be crushed whether you agree to it or not. I've seen counties do it before.