Training for the 100 fly?

I'm seeking advice on training for the 100 fly. Decided to start swimming it last year. Swam it 7x on the three courses. I can only remember 3x times where I didn't suffer from complete paralysis the last 15 meters or so and worry about a DQ. Gah. So how can I fix this? I've read that you don't need to train fly in practice. I'm not sure I buy this. The muscular fatigue from fly seems unique. And I don't want to substitute freestyle training for it. What are some good sets? How many SDKs per length should I take to prevent oxygen debt? If too much fly hurts the shoulders, is kicking a decent training substitute? I also seem to swim better 100 flys on a week rest. The paralysis seems to be associated with a 2 week taper. Does aerobic fitness drop off that quickly? Is this an age thing? Or is it that I just don't train enough yards for a 2 week taper?