Our new Heartland Prowler doesn't have a tire cover as the spare is mounted under the trailer.
However, our previous 2013 Heartland Trail Runner didn't come with a tire cover, but I did purchase one for it, as I did (several times) for the trailer we had before that.
We usually got about two years out of them before the elastic either gave out, or the vinyl started cracking (dry rotting).
I still have the one I bought at Camping World for the Trail Runner as I had just bought new wheels and tires for it (larger than the stock ones) before we traded it in and the tire cover was too small to fit the new spare.
Since you are under warranty, you should contact your dealership and let them know, although I will tell you that when we got our Trail Runner, the bumper caps kept falling off as did one of the sewer drain handles on our first trip out, and they were not covered under warranty.
By the by . . . which Heartland trailer did you get?