now that the machine has arrived safely, here is how we packed up a very different sewing machine.
We built a base that fit into the bottom of the box - it was set on top of 1" insulation foam.
The machine was bolted to this frame - our concern was that no weight would be sitting on the oversized flywheel.
The box was custom made - DH went dumpster diving at the appliance shop in town (with permission) and pulled out several large boxes from TV's. Apparently most kitchen appliances no longer come in cardboard boxes, but the TVs are now big enough that he got plenty of heavy duty cardboard. Then he cut and folded it to create his own box, using high strength spray adhesive to glue it shut.
Foam packing was put between the box and machine, and filled up so that it was not possible for the machine to shift in any direction.
This box weighed in at 60 lbs, and was cheaper (and much faster ) to ship UPS than USPS. For comparison, we dropped this off at UPS at 5:30pm (they are only open from 5:30 to 6pm for drop off) on Thursday the 13th, and he got it yesterday. Earlier this year, SteveH shipped a regular sized machine to me via USPS and it took almost three weeks to get here. Not sure if either machine had a lot more miles on it or not, though with USPS the machine went about 300 miles past my house, and then turned around and took the long way back.
And we did stick some bubble wrap in there - especially for SteveH since we know how much he loves the stuff.