Fred,
I believe that tubes should definitely be well packed and shipped separately. If any tube comes loose during shipping it is going to do a lot of damage.
I would let the buyer know the tubes are being shipped separately and maybe tape a card over the power cord prongs with the same message on it.
If the buyer doesn't even know how to install the tubes I hope you are not offering any type of guarantee on the amp. If he doesn't know what he is doing and decides to peak the plate and dip the output the amp is going to be most unhappy
Sort of like the caution note in a Panasonic printer I bought at the dawn of the PC age, the first warning in the manual read literally: "for Mr. printer to be most happy please do not drown him in the bath tub" which roughly translates into don't get Mr. printer wet or he will be p**sed.