In some years Colemans were OEM, but Airstream still put them in a drain pan and used the hidden drain. You should have a black hose that hangs out of the road side of the trailer just in front of the wheels. This is where the drain water would come out if the tube was connected to a pan.
You can order a pan from Airstream for an AC but the only one available is for a Duo Therm Penguin. I belive Inland RV was designing some for other models but you would have to ask.
WBCCI #5501 AIR # 49
1978 Argosy 28 foot Motorhome
Wise men talk because they have something to say; fools, because they have to say something. -- Plato