Never done it on an airliner because I've not yet had the pleasure of flying an airliner but have done it on a BN-2 Islander in the Caribbean. Seats out, box in. Came from NY to St. Maarten, N.A. en-route to Antigua. I seem to recall being told that the cost was the same as a standard ticket but she got to lie down the whole way. I'm sure the loaders/unloaders of the big a/c did it fairly competently but I and a company helper had to manhandle the very heavy box (thrice layered and sealed within a metal box inside the absolutely huge aluminium outside coffin) into the BN-2. The only way in was slightly on end, definitely on the side, with some ominous clunking noises from inside. Rather glad it was a daytime flight!
There was also the "morgue smell". Hard to describe but I guess they try to provide a sort of frankincense-and-myrrh athmosphere to the proceedings. Of course the other end was even more shambolic as we had to wait for the completely late undertaker to turn up in what looked like the hearse out of the Jamaican Bond film (don't remember the name), with the sun beating down on box and getting behind schedule.
No idea what she looked like when they opened it up for family viewing but she probably needed a hairdresser after being turned upside down and sideways.
Not really my favourite flights but the customer is always right, especially when you're doing charters.
Thought for the day!
el dorado