As one who just made a dust cover for my Webster Cecelia out of purple velvet, I highly recommend making one. I taped a bunch of lightweight paper (could use tissue paper but we had some packing paper here) together to lie the harp down onto and trace around it. Then I measured out 2 inches along the top of the neck and down the sides. I also measured half the width of the back of the harp and went out that far +2 inches in order to have room over the widest part of the soundboard. Voila! I have a pattern now I can use over and over. It was so easy. I sewed strips of velcro down the front opening, making one side of the opening about 3 inches wider than the other so that I could have a flap.
The velvet was kind of icky to work with on the sewing machine because of its nap, but other than that, it was really very easy…..and it’s quite pretty.