Thanks you guys for the comments.
Yes, the rear seat is simple. I use the electrical tube to reinforce and connect it to the frame. It's been working very good. My wife who weights around 120 lbs been riding on it for about 10 hours with no problem so far. We can hit 30 MPH on flat street and climb up the hill in San Francisco with no problem and it is so much fun to ride with the passenger.
Here are some pictures. Let me know if you have any question
Hope it helps!