Car covers seemed to be a good solution to atmosperic gunk in the earlier 1970s, when I first started paying attention to car cover ads. But as mentioned, they do need to breathe, even the thicker ones so that condensate/moisture can escape/evaporate through the fabric. Moisture needs to go both ways, in (to a lesser extent) and out (to a greater extent) for best results. Paint erosion from a fluttering-in-the-wind might not be a critical issue for your vehicle, but it can with others.
Many covers have a drawstring around the bottom and even some have a hole for a lock cable to fit through down there, too. Might also need some inexpensive ratchet straps over the hood and deck lid areas, too, with the hooks placed gently to the sheet metal, for best results.
As for your rear window plug area, might be best to get some thicker clear/opaque plastic sheeting and tape some of that to the body, over the rear window area. To deflect and water-seal that area, for best anti-water-intrusion efforts.
On some car cover websites, they have sizes of vehicles mentioned. 1 to 5, usually. Even some references to wheelbase and length, too. I suspect your Imperial would be the biggest size available!
NOW, some other things to consider! Animals who might use their claws to play with the cover fabric and climb onto the vehicle itself. Or some smaller critters who might get under the cover for shelter. Damage? For the cats, their claws will shred the cover in short order. For the smaller critters, no telling what they might do as they seek shelter.
Back in the 1990s, a lady came in one day seeking a car cover for her new Suburban. I gently inquired "Why?". Seems her cats were sleeping on the vehicle at night and her husband did not like that, being concerned about paint erosion and claw scratches. Knowing how the cats we had did things, I advised that a cover would not keep them off the vehicle's top. PLUS the effort it would take to remove the cover each time she left the house, where it would be stored in the vehicle, and having to put it on each night. A lot of labor for a large and taller vehicle! She was about 5'5" tall. She had not considered those things, unfortunately. "A car cover" was her obvious answer to the issue, until I mentioned the many side issues to a car cover for such a large and tall vehicle. Fortunately, GM Accessories did not have a car cover for Suburbans back then, so she had to look elsewhere OR consider a different course of action.
I tend to agree with
@Big_John, a rented garage might be a better solution. But many of those are now going for $200.00/month and up. "Car does not run"? A roll-back wrecker and an operator who knows how to use it, plus some "roller skates" to help position it in the rented space (about $200.00/pair, depending upon the type and such). That "lock it up" space also keeps the car protected from possible code enforcement issues, too, especially of the tires might go flat during the non-use periods.
MANY side issues to using a car cover, from what I have seen. YOUR determination, though.
Building a quality garage, even if it might be used for a few months, should increase the value of your property, if it's done right. Might not be such a bad investment?
Just some thoughts,
CBODY67
