PB and DocB have this down to a science. This is my method and I move every three years with the military. First, remove the tubes. If you have oversized caps that are not secured in the build, you need to do so somehow. Blue painters tape to hold the top place to the base. Card board around the transformer extending past the top of the transformer bell housing. I usually save the cardboard that came with the kit for this purpose. Large bubble wrap and a double thick cardboard box. Sticky small bubble wrap.
After you tape the top to the base and protect the transformer, I wrap the entire amp with sticky bubble wrap (small bubble). Put at least two inches of large bubble wrap on all side of the amp in the box and use more large bubble wrap to make up for the difference in transform height to base. put the amp in box with the transformer and top plate down. Tape the box on all sides of the lids. Mark the box with Top and don't place on side or something similar.
This has worked for me over many moves with gear in the past.