Bubblewrap, lots of bubble wrap.
-Place a sheet on top of the wood base and push it into the corners, then set the chassis plate on top.
-With another two sheets wrap them around the amplifier in each direction.
-Next step is the most important, get some packaging tape and wrap it tightly around the amplifier. I usually do three strips, one across the power transformer, one across the volume pot and headphone socket, then another length wise. Each strip is a complete loop around the amplifier. When done the chassis plate will be held very tightly into the wood base protecting the elecy bits, and the wood base from damage.
-For the tubes i usually find a small box to fit them into with layers of bubblewrap around them.
-Final step is to find a box big enough for the bubblewrap ball and tube box you have just created, then add more bubblewrap around them to fill the box so they cant move around freely inside it. I like to have at least 3 inches of padding between the bubblewrap ball and the box.
The more packaging you use between the amplifier and box the better as it will get thrown about by couriers. Expect it to get dropped from chest height. I have shipped over half a dozen this way and despite the few torn and crushed box's, and one arriving soaking wet!, they all arrived intact.
