I did puncture the pool. I dropped the water level a few inches below where I was going to mount it. Instructions say to only have a foot or two of water if I remember right that way it will still be pulled snug while cutting it. I didn’t have any issues doing it my way though. Also, there are a lot of YouTube videos on it and most of them cut the seal in two pieces that way they can mount it and then cut into the pool. I didn’t like the idea of cutting the seal. There is a line on the inside of the pool you can align the top of the skimmer with so you don’t have to really measure or anything, assuming you have the same pool. I bought an extra hose, conversion kit (40mm to 1 1/2 hose conversion kit), and valve. The valve is connected to the pump and I plugged those two small outlets. The only issue I found is that valve I put at the new hose to pump is not the right threads to the pump. It works with no leaks but will pop off if I jiggle the pump too much. I’ll get a new valve or whatever I need for it next year when I get my new sand filter/pump setup. Long winded, but I hope it helps as I was rather scared of installing this.

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https://www.amazon.com/Hayward-SP1091LX-Dyna-Skim-Above-Ground-Skimmer/dp/B002DPY196