I have bought several machines from Shop Goodwill, but only where I could go pick them up. I surely would not trust a Goodwill packing job.
On one of Patsy Thompson's FMQ DVDs,"Fast & Free" volume 2, her husband shows how to make your own plexiglas extension table. Your public library may have that DVD. Somewhere I have seen a photo of extension tables made from wood, probably saw it on the "Vintage Sewing Machine Forum" on here. In a pinch you could even make a cutout in a cardboard box. Keep all the parts together, you never know what will show up later.
Buying sewing machines from thrift stores means you often don't get the extension table or power cord. I have several of those old fold-up tables that appear to have been made for Vikings. They are not a snug fit, but do work well with other brands and models of sewing machine.
Good luck. Please let us know what you come up with.