Oakmaiden - rather than sewing the elastic on first or last, how about creating a casing, either by turning up a hem and topstitching, using a lycra strip as a bias, or if you line your pants, sewing lining and fabric together wrong sides together, turning right way out and topstitching about 3/8 away from the edge to form a casing. Sew your net on and then thread elastic through the casing and close your crotch seam.