Wen I was selling antiqes on ebay, sometimes I would use swimmers noodles, cut to fit, around a bubble wrapped item, never had a complaint. However,prior to using them I once shipped a crockery whiskey jug ( old & empty) and at the post office, I saw the conterman throw it onto a hard surface from about 6 ft away. I just knew there would be a claim!
Dang, when I was desperate...I even used a cheap cut up styrofoam cooler to fill the box...I've shipped some very unusual items but you sewing machine experts have my admiration for your moxie just for shipping old sewing machines.
adamae