The clay form is covered with a couple of layers of saran wrap. This makes it much easier to pull the mask off the clay and keeps the clay from sticking to the inside of the mask.
The horn has to be smoother so lay it on first with half-inch cotton bedsheet strips, cut diagonally. Keep laying the strips on and painting with epoxy until you have a layer or two covering the whole horn.
Then cut the burlap in diagonal strips 6 inches wide and start laying it on, keeping it in place with pins. Paint it with unfilled West System epoxy. Don't worry that the mask is rough with burlap ends sticking up here and there. You can easily sand it smooth after the glue is dry.
It takes a lot of epoxy to saturate the burlap but a single layer is really strong enough, don't make the mask too heavy. One advantage of a thin mask is that you can see right through it, the epoxy is clear and the mesh is open.