I originally wanted the route to be by sea, from Southampton to Marseilles, and after a brief stop there, onward to Alexandria and then on to Cairo. Is that route plausible? Was it more commonplace to travel by land across France by the late twenties? The characters are on the run after stealing a rather precious item, so would the sea route confuse their pursuers, if travel by land via train would be the usual method? The ship they would be travelling on wouldn't necessarily need to be exclusively a passenger ship, they could probably talk their way onto a cargo/mail ship just as easily.
I've Googled, Wikied, and even checked real live actual books, but nothing gives me definitive answers or specific detail about that precise route on those dates -- the closest I've found is information about the Indrapoera.
Any and all help is greatly appreciated!