The one i used isn't on their site any more, it had a 1 piece felt covered plastic cover, which had no holes, so you pretty much just had to guess where to cut and it wasn't the easiest thing to work with. Mounting to the wood was a piece of cake though, it had very good directions of where to drill in the skull to match the wood bases pre drilled holes.
I see the ones they have now are either a two piece cover that the two halves overlap which looks much easier, or a leather cover which solves working with rigid plastic.
Even with the plastic it wasn't hard to do, it was more work preparing the skull and antlers than it was actually mounting them on the base.