Are you looking at a new 2014 on the lot? I don't know if this holds true as it did for the 2012s when the 2013s were on the lot - but at that time, a little over 20% off sticker was reasonable. With improvement in the US economy, the increase in sales of Airstreams and the investment in the new manufacturing space there, I'm not sure whether you can still expect that. If its the right one for you, ask what their absolute bottom line is. If you're happy with that - snag it and enjoy the heck out of it :-)
Alternatively - set your own price at X% off sticker. Offer that and be prepared to walk if they don't like it. While they likely don't want to discount deeply, if its at the dealer - they've already paid for it and they'd love to have the sale before 12/31/15.
Good luck - let us know how you do!!
Oh - and yes, the world's most interesting people own Airstreams. Ask me how I know :-)