I think we may have misinterpreted your "storage cube"
@Sew What? The interfacing/ fleece goes between two layers of fabric - outer and lining. If you're going to use faux leather or some other pvc equivalent and the inside won't show then I wouldn't bother with a lining. However, pvc isn't the easiest to sew, certainly on my Janome and I have to use a walking foot or a Teflon foot. I don't know about your Pfaff but others here may.
Just to add that when I've made dust covers for machines I've used some heavy linen upholstery fabric, once a thick scuba - all unlined - and they do the job.