Make sure ALL the meat and fat is off the quills. Just bare quills and skin. This takes a little time but if there is meat left on, or the yellow fat, You are inviting a dermiste beetle invasion. You don't want that because they can then attack any mounts you have in your house. You won't notice them until it's to late.
I'm a taxidermist and I clean my tails completly and then spread them out in whatever pose mount I'm doing and then spread bondo on the quills, let set, flip over and spread bondo on the other side of quills. Once hardened it is permanent and no bug issues. Hope this helps. Feel free to PM me if any other questions.
Jim