Since you have it done, this is more for peace of mind. They're more resilient than you'd think. As long as it ships right side up, and you packed it where the amp is tight in the box but there is some "spring" to the package when you shake it or drop it from a 1/4" or so, it will be fine unless the shipper does something stupid with it.
Last couple of amps I bought from the factory shipped in just one box, tubes in, but suspended in with foam corners and additional cardboard to make sure the amp didn't shift in the package, and two of those came from Germany. I also shipped a BE50 to Cali and back twice, and it was packed that way.
After destroying an amp due to stupid packing myself, I subsequently used to pack them like they were going to be dropped from an airplane. After buying a few amps from Friedman, I started packing them like they advised. The vast majority of the winning the war is making sure it can't shift in the box, that it can absorb a normal amount of shock from getting jostled around, and doing what you can to make sure if the shipper ignores the label and stack shit on it that it will distribute that load as evenly as possible without stressing any tender bits of the amp.