Sundowner (2up) in my 2007 FLSTC was the cure for my lower back pain. No backrest needed. But, to be honest, being seated just over the oil tank is like being into a frying pan
BlackG30,
I agree with the oil tank location, worse possible place for comfort. I also have the 2 up Sundowner Seat on my Heritage and find it is much better than the stock seat but I am considering a backrest as I have a tendency to slouch after being in the saddle on longer rides and think it might help even more for back pain. The heat deflectors by RJ's Orininals help greatly reduce the heat off the oil tank :s