They fold down very easily. There is a nylon strap near the top of the seat cushion and you just pull them down. I haven't measured how large the opening is but is large enough to ealsily access the box that holds the 12" sub box that is in my trunk. I would guess it is about 16" or more. I could crawl through the opening if I had to. I am also a slight, small person, lol.
I will be working on my first gen tomorrow. If I remember I will snap a pic.