Shipped two amps in road cases with no additional packaging, and received one amp in a road case with no additional packaging. All transactions worked flawlessly. Amps arrived safely and the road cases seemed to have been treated really well.
I shipped a Vibrolux once in a lite duty case but with xtra padding I added and it arrived like it had been thrown down a flight of stairs, the handles apparently gave them more means of achieving a better trajectory. Also the case having wheels caused more problems for some reason. Never again...
Never had a road case but if I did this is what I would do - Buy a couple cheap locks and lock it up. Then send the keys through the mail to the buyer. This way when the amp arrives he has keys to open it and no one can mess with it unless they cut the locks.
I've heard (from people that work at the UPS sorting terminal here in Louisville) that the wheels do cause problems on the roller line things. This does make sense - imagine trying to push a roadcase with wheels down rollers that are made for boxes. Now imagine those rollers being 10 or more feet off the ground which is also often the case.
Shipping it in the case is great for protecting the amp, but I'd take the wheels off OR find a cardboard box to put the case in.
UPS and Fedex charge a little more for not being encased in cardboard and unusually shaped items because they may not travel well on their conveyor systems. They also charge extra for extra large items so be sure you check all the additional charges.
If you want to make it look more "boxed", I'd recommend just getting some thick cardboard and use strapping tape (clear stuff) to cover the road case. Leave the wheels so it can be rolled around. You might also make cut outs for the handles but cover up the locking mechs. I haven't needed to ship something in a road case but I do have some of them. The best one I have is an Anvil that fits my Deluxe Rev. and I paid $5 for it at a garage sale.