Just to give you an idea of needed space, I was able to fit my GC into a mini van if that helps. I layed my slate flat but a mini van rides much smoother than a U-Haul truck and I only had to move mine about 30 miles. I kind of think of slate as glass, brittle and fragile in the flat direction so I would think for long distance you would be best to freight it standing up. 1 1/2" -2" thick 4' x 8' sheets of styrofoam insulation (pink stuff is higher density than white stuff) is pretty reasonable at home centers and can be easily cut to desired sizes for protecting slate in transport.
