Folks...
Can't offer any advise on large tanks...travel regularly with small RB tanks 3AL 19's...with valves off...tank tops covered with clear packing tape...valves sealed in zip-lock storage bags...I identify the suitcase at check-in as being filled with dive gear...
Maybe I've been lucky...but I've never had a problem...RB travels as carry-on...
As an alternative to travelling with large steel tanks... travel with a doubles manifold...7.25 in. bands/bolt assemblies and make up a set of AL doubles at destination with rented AL 80's...I know several divers that do this...you will need a little extra lead time at the destination LDS to set up the doubles...and a small ratchet with a short ''socket extension...
One of my guys happens to be in the shop now and advised one destination LDS offered to buy the manifold and bands...so there was no disassembly and removal at the end of the trip...
All serviced tanks leave my shop with valves ''hand tight'' only...no wrenches ever...Big K bank cylinders...with tapered threads...different story...
Best...
Warren