Marley,
First off, congrats on your upcoming hunt. I agree with what what one dude said. Way too quite on the board about sheep hunting. WE NEED SOME SHEEP ACTION !!!!!!!!!
Ok, here is what I did in 07 flying out of Fairbanks. I salted my cape well, and rolled it in a plastic bag. I puit that, and the horns in a Rubbermaid tote I bought at Walmart. I also put some other things in it to get the weight at 50lbs.
I have heard of guys carring their horns on, but I doubt my horns would fit under the seat. Granted they were no huge set, 38x13.5, but big enough to cause a possible problem.
Take lots of pictures, and have a great hunt ! Looking forward to the story upon your return.