I do not recommend using Press N' Seal! I had the same problem as Betty--and didn't even use the sharpie but an washable Crayola marker! And you sure can't do much dense quilting on it or you can't get the dang stuff out.
I use white chalk pencil, pounce chalk powder with stencils, sometimes the blue line marker (water soluble). Also, if you have a laser light on your LA machine, you can usually move it to the front and using a board (or large cookie sheet, etc--I have a plastic shelf I got bought from DeLoa Jones) on the quilt with the stencil or picture laying on it, trace with your laser. It's a little tricky to get placed just right, but well worth it.
JustabitCrazy--where do you purchase your black light chalk/pen?