Home of the Horse Trailer Blue Book
Some old threads on "Walk Thru Doors"...
http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=11069
http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=11345
http://www.horsetrailerworld.com/forum/thread-view.asp?threadid=11438