Hey Chris, great to hear from you. I hope you and yours are getting buried by too much snow these days!
I have a lathe, but it's pretty inaccessible so that's why lazy men approach with hand shaping pulls. Actually for these I made a stop cut around all four sides of the bottom edge of the pool, and then used a chisel to shave off the waste. That's a little faster than just trying to shape everything with the rasp.
Cheers, Mike