How do people go traveling with mals or sups on airlines?
Is it any easier/cheaper on any particular airlines?
I'm looking at Sri Lanka, Maldives areas to fly to, any advice appreciated.

Top of mind stuff below

The board is not an extra bag, it's oversized sporting equipment. Pay for the extra sporting equipment/baggage option in both directions when buying airline tickets and your life will be better at the airport.

Do not pinch pennies on a board bags. There's one thing that baggage handlers hate more than their jobs, it's your oversized lump of crap that's making their day worse.

Ideally don't put paddles in the board bag, I've had a few indentations...

Check the maximum cargo length the airline will accept. Most surf destinations are use to having boards go through the system so normally no issues.

Don't underestimate lugging the gear around when you arrive, particularly if you are going to a remote location. Travel with rack straps to secure the board if needed.

If you're well prepped and calm through the process its generally a walk in the park.

Don't fly with this pair!!!

I flew to Maldives last year with a 7'6 SUP on Singapore Air with no problems

And to add to Brent's - try to be shorter than max. I've repaired boards with very obvious door slammed on the tail to make it fit and more than once too

Thanks for the advice guys, general web searches got no useful info.
Cheers.

Buying the Severne bag with wheels has made traveling through airports so much easier for me.