Many require pelts from Legendary Animals as well as perfect skins from other animals in the world.
The Trapper has a variety of outfits, clothing, items, and equipment that he can craft if given the right materials. This location is only accessible after Chapter 6. Follow the river that heads down Tall Trees, and look for where the road curves East to climb the hill, where you'll find the Trappers location. A fifth Trapper Location can be found in the far south-west region of West Elizabeth, far to the West of Blackwater in the region of Tall Trees.