For packaging materials, try the recycling dumpsters behind optical stores (big chain stores are best). They frequently get new glass-shelf displays, which usually come packed in large quantities of polystyrene foam (photo shown below). This is the perfect material for packing large, heavy, fragile items....it will compress slightly when heavily stressed, but it will not collapse, break down, etc. You can easily cut it to shape with a serrated knife. I have collected this stuff for years, and have several Hefty bags of it in my garage. All free, too.
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+1 on Polystyrene
Best stuff there is.
I collect it at work.