You can find how long they have been in business by reading the material on their websites. Born Free and Coach House have been around for quite awhile. The BT Cruiser is a model, not a brand name, and is built by Gulfstream RVs.
Born Free and Coach House are highly respected brands but you don't see a lot of them on the used market. Actually, you don't see a lot of Class B's on the used market. When and if they change hands, it is often privately. You can search for private sales via web sites such as rvclassified.com and rvtrader.com.
I have no personal experience with any of them - never owned a Class B myself.