Go to any building supply store. Sheets of home insulating foam are sold($7 to $10) in 4x8 sheets in 1/2 or 3/4 inch thickness, With a box cutter or good sharp knife, you can cut, fit, tape and glue(I use the spray type of glue, better contact and dries quicker) this foam to virtually any configuration you need. I do a lot of shippin, and I have had no problems since I started cutting this stuff to fit my needs.
Packing Peanuts-a waste
Why do people use packing peanuts when packing a heavy item such as an amp or speakers? Many of the MBE packing places rely heavily on this things. If you think of it, what good will they do when a 50 lb amp shifts. All they will do is crush and flatten.