Had lots of international flights and vehicle transport rides with the family and usually two SUP's in the one board bag plus two paddles in another separate paddle bag.
Upon check in I will strap the paddle bag onto the board bag carry straps yet check them in as separate luggage in case they get separated.
I have never had a problem with travel damaged SUP's or paddles.
Love a split pool noodle on my board's tails and nose, sometimes on the wide point of the rails if I'm organised enough.
Happy travels.
Regards Jack