First, you need to get the hide off. You'll probably need to soak it in water for a couple days, and the smell won't be pleasant. After that, cut ALL of the meat away. It helps to apply some borax, wait a few days, and I like to grind away what's left with a Dremel, once it's dried. Then, you need to remove the horns from the cores and clean the cores. Place the whole thing in a plastic bag for a week or so and they should pop off, though may take some persuasion. Clean the cores well and bondo the horns back on. No matter how clean the skull plate is, bugs will still get in the cores if they're not removed and cleaned.
As for the fox tail, pitch it. It needed the bone removed and then it would have needed to be tanned. There's no way to save it now.