It's the power valves that are most at risk; the pre-amp valves should be OK, and can stay in their sockets. A higher risk, though, is the weight of the transformers in there, in case of a hard knock, such as dropping the amp. This weight can rip the trannies from the chassis, or twist/bend the chassis. There's not a lot one can do to protect against this except make sure the amps aren't dropped..! For my part, I'd take the amps myself, and make a day of it..! I did this recently with my Hiwatt, taking it for repair implied a 300 km round trip. I have to go back shortly to collect my Fender Bassman 50, waiting for me after overhaul since Christmas. Now that the French curfew is extended to 21h00, I can plan such a trip. I wouldn't want to send my amps by courrier if I could do it any other way, and it's cheaper..! Your move may vary, naturally.