I went to this event last Sunday. It is primarily an indoor event (good considering it falls within the rainy season in the Kanto area). It is interesting they ran the special trains right into the maintenance facility, and unloaded passengers using the inspection catwalks. Seibu ran a morning special train from Motomachi Chukagai,replacing the traditional special from Seibu Shinjuku Station. As I mentioned in another post, this event had the greatest number of vendors/representatives from other private railways as I have seen to date (admittedly, I have mainly been to JR events so far). I could only hang around for the first 2 hours, as I had to catch an afternoon flight back to Hokkaido from Narita AP. Otherwise I would have caught one of the afternoon shuttle trains back to Hanno, or the return special to Ikebukuro.
Youtube contributor karibajct's coverage of this event: