You need to buy an Antler mount form from any taxidermy supply store, I buy from McKenzie.Set your skull plate in the form to see if it needs shimmed upto make it even with the top of the form. If so, you can place a small block of wood under it. Next, I use Dura-Bond 15 minute powdered drywall mud, mix it with water to make a pretty thick paste ( not runny ), and place a small ball of it in the form where the brain cavity of the skull will be. Drill 2 holes through the skull and screw the skull plate through the wood block and securely to the form. Next, use some of the remaining drywall mud to cover the skull and smooth out ( you can wet your finger with water and do this )to match the the form. Let this set and dry completely ( over night ). Now you can cut your leather to fit and use a staple gun to attach it to the back of the form. I cut mine in a sort of broad looking arrowhead design and it fits great. If you want to email me ( [email protected]), I can trace the design for you and email it to you.
Good Luck!!