Maybe sharing what I do can help Kimela and elicit constructive advice for me. I fly several times the Earth's circumference every year for diving, but mostly work :/
I've got two packing permutations.
OPTION 1
This is for basically "dive only" trips where I don't have to use up carry-on space for things like business clothes.
Almost all dive gear goes into a big North Face Base Camp duffel (BPW, wetsuit, fins, DSMBs, spools, and other tough bits). Bits of clothing are in here as well, usually in packing cubes. This is checked in. This duffel is also my boat/ shore bag. I strategically pack with wetsuit covering BPW, fins as "barriers" and wing partially inflated. I figure the last part may save from pinch tears. From lots of flights, things arrive as perfect as they should.
Regulators, masks and other fragile things are carry-on.
OPTION 2
I basically dump the duffel as packed above above into a Briggs & Riley check-in suitcase. Maybe fins taken out and put alongside the suitcase's interior as barriers if I'm not lazy. The difference is that I also include a Pelican case in the suitcase just big enough for my regulator set (I may stick masks and some fragiles in as well). I'm a bit concerned about airport security mishandling regulators and such, but so far so good. This allows me to carry on pressed business suits, dress shirts, etc. I don't get my business clothes pressed at the destination as that takes up time.
For either permutation, I'll have inside my carry-on a small, lightweight waterproof bag (the kind that has a roll up top). Inside are various dive-trip bits, like sunscreen, cert cards, save-a-dive/ first aid kits, etc. I bring this to the boat/ shore. Also, both permutations are compartmentalized meaning they do not require any repacking once I arrive into the hotel, just grab the right bags in the morning and go (duffel and waterproof bag).
@Kimela: my setup is generally water resistant (have been through monsoons, etc). But the key aspects for water resistance are the duffel, Pelican case, waterproof rollup bag, and packing cubes. The suitcase basically just sees the airport, the inside of whatever mode of transport and the hotel. If needed, you can just pack a lightweight rain cover (a garbage bag will do). Plus, it's mostly dive gear ... getting it wet isn't the end of the world for me