Yes Judy I have one and it was here when we bought the place. Mine is not the cover-all brand though, it is written "tempo" on it and I have no idea how old it is, but it's in great shape and the covering isn't the flimsy type that are used lets say if you want to store a boat or a car, if you understand what I mean. At first we used it to store 800 large squares bales of hay but now that I have lessened my work load and have gone to round bales I was free to do what I wanted with it. I love mine and am perhaps thinking of putting a second one on my property, maybe not as large as the one I have now. It is approximately 24 feet x 36 feet. Because Blue our saddlebred came home from the trainers and I had acquired my arabian rescue I was left short of stalls in my "barn". I built three LARGE stalls in the cover-all and have Abby, Storm and Crystal in there at the moment, until Mike gets my SECOND BARN UP, DO YOU HEAR ME MIKE!!! I have all the material sitting there he just "hasn't got around to it yet!!!
So I decided to use the cover-all. As I said they have 3 large stalls in there with floor for them and shavings. The front is totally enclosed with the exception of a "door" that I can shut, so they can come in and out as they please at the moment. The entire cover-all type building I have is fenced around it so the horses can't do damage to it and it also has a large gate at the front of it. Of course when the cold weather flies they will be locked into their stalls at night. Also besides the stalls they have a large area to just walk around in inside and I plan on putting a round bale of hay in there, they also have a watertrough in there so they can get out of inclimate weather during the day should they choose to do so. As far as temperature goes I don't have any idea yet. I believe it would be no different than a non insulated barn but don't forget minis get such a coat in the winter time it's probably healthier for them, as long as they are out of the wind and have plenty of hay to keep them warm. Now having said that when and if we get temps this winter of -20 celcius or worse, than I will have those three come into the barn at night, I have a large open section of about 15 feet by 20 feet and my entire barn is rubber mats so I can throw some shavings down in that area for them if they need to come into my main barn.
The great thing about the cover-all type is that you do not need a building permit for them, not the one I have because it could be moved, not that I would do that. So for me, this set-up works and the horses seem happy to be able to, for now, come in or out as they feel comfortable with.