I used a LOC Expediter with the transition converted to an alt bay for my L2. It wasn't initially built with the intent of being my L2 rocket, but after several successful DD flights on big I motors, I simmed it out and realized it would work quite well. And it did. The success of that rocket led me to having the confidence to scratch build a few HPR rockets. I understood the principles behind the designs very well prior to that, I just never felt I had the time or the tools to scratch build something. After that L2 flight, I realized I had everything I needed. I still don't scratch build too many things...I'm just not that creative...lol