I’ve used this method several times and it’s always worked out fine: I turn up at the airport, back pack ready to go (as if i were just about to hit springer!). When you check it in they will look confused. Ask them to give you an airline plastic bag, they usually have them at the desk. It’s clear, about the size of a large trash bag and has the airline logo on it. That’ll keep it from getting wet between the plane and terminal buildings.
They may just point you in the direction of outsize baggage but you can ask them to do the same thing. Just make sure of the obvious, straps secure, contects secure etc. It’s also really easy to spot coming along the conveyor amongst all the flatlander suitcases :happy
Cheers
Cheers