Ace went for his first trailer ride yesterday, and all went well. We tied Copy and left Ace loose, and just drove about 2 miles around the block. He seemed just fine. I didn't hear any fussing back there, and the trailer hauled smoothly.
Afterwards, I took him out of the stall alone, led him around a bit, then tied him to the wall for five minutes. He did call for Copy, but was pretty well behaved. Then we went to visit each of the other horses, and then turned him back out with Copy. We are taking baby steps towards getting him disconnected from his Mom so weaning will be less traumatic.