The easiest way to change the tank pump for me, was to pull back the carpet and cut through the plywood / foam / aluminum sheet composite floor with a skill saw, finishing the corners with a hand saw. I triangulated on existing penetrations then drilled a small hole to make sure I had the right spot, then cut out a square about 10 inches on a side at a 30° bevel. The plug pulled out revealing the pump.
After The change, I glued the plug back in with expanding foam and left a note for the next owner explaining how to get in.
