While the exterior seal on the cooler is drying, make the winter flaps.
This project calls for two (2) flaps per shelter.
I always make four (4) flaps per shelter so that I have backups in case of accident or loss.
Measure and mark out four (4) 10" by 10" squares on the sheet of pond liner.
Using the rotary tool, utility knife or fabric scissors cut out the squares. I highly recommend using a rotary tool for cutting the flaps and in the step 10, the strips on the flaps. This is the most effective tool and your wrists will thank me too.