I'm the one who started the thread but don't keep up with it and often miss messages on this thread, as well as direct messages sent to me. If you want to learn more about Altos, I suggest you join the Facebook group Altoistes. Submit a request and then keep an eye on your "other" message folder, where message requests come in from people you're not Facebook friends with. Then just respond to the message so we know you're interested in these cool trailers and not looking for a group of Alto singers.
The group is the place to go to learn from current owners and to hear of any rare used trailers that may pop up.