I would never fly with a synth, that's what local rental houses are for. In my 4 decades of gigging I have never known any professional gigging synth player who wants to travel with Synths via air. Putting your synth in your luggage? Wow, you actually do that? Why?
It's dead simple to rent a Motif or Montage pretty much anywhere, and the promoter can easily provide it. Even back in the 1980s and 1990s it was dead simple to rent a DX7 to use a controller for your rack synth
As for local gigs which is what I do 99% of the time so I can sleep in my own bed, I have a hard case for my Montage. It fits and sits great on a portable foldable hand truck in the back of my SUV. As does my two tiered stand all held together with a bungee cords. It makes for a dead simple load in, and I don't have to carry anything but my backpack