I’ve been flying with surfboards for decades and I have yet to have anyone pull out a tape measure at the desk. I suppose they could though. Mostly get ready to pay whatever they ask and be nice. Smiling and joking with the agent behind the desk will make them want to work with you. Doing the opposite will get you into trouble. Being nice got my boards to Costa Rica for free once … six boards. On board bags, there are lots of good ones. Look through what is available and pick one that looks like it has good padding. The shop owner should be able to give you good advise. Those guys almost all travel a good bit.
I have not flown Continental with boards in about 15 years, back then we did not have any problems (CA to Hawaii to Australian). I have had a lot problems on United to Hawaii though such as: looking in bag and charging per board, weighing the board bag (they said it was a 50lbs limit, that was this year by the way), and one time they claimed they saw something under the glass and wanted to break it open.
I have flown Alaskan, American, Taca (Lacsa), Aero California, America West, Delta without out any problems.
The 115 rule depends where your departure is from, I’m finding. I’ve had them pull a tape out on a 9’ Board bag before. 10’ might not make the flight. (I wouldn’t chance it.)
My suggestion would be to contact one of the freight companies and ship ahead. It’ll be a safer bet and you might pay a little more but then Continental charges $100 each leg.
A Balin or FCS Coffin Bag would be good…but pack it good. Protect your rails, deck and hull. Lots of bubble wrap and foam sheeting helps.
Your best bet would be a Surfcase if you can find one. Good Luck.