LindaShipper, I don't mark my quilts often but I do mark when making them from time to time. I like the pens that erase with heat too. Just ordered a bunch of white pens from Amazon. Fairly cheap too. I tried them out on navy fabric, took the iron to them and it erased just fine. Just checked the fabric again after a couple days and still gone so I'm happy with them.
Heat Erasable Fabric White Marking Pens with 20 Refills for Tailors Sewing and Quilting Dressmaking, White Heat Erase Pens of Fabrics.