5 cross piece are wired to the underside of the arches. The purpose of the cross pieces is to align the arches relative to each other. A 10 inch wide length of corrugated cardboard is placed on top of the arch covering the full length of the arch. Heavy string is then used to stitch the cardboard to the poles. The cardboard is covered with plastic food wrap whose edges are folded around and under the edges of the cardboard.
Tape is used to hold the edges of the plastic in place.
Snow sprinkled with water can then be placed on the arch and left to freeze solid. That way the strength of the arch gradually increases as the weight of the arch increases. The arch can be made the size that suits you. The ends of two or more poles can be lapped about a foot and wired or securely tied to make longer poles for bigger arches. The ends of the arch are held in place by burying them about 6 inches in the ground.