The initial cuts were made along the red line and then on the seam on the back of the tank. IF I were to do this again, I would cut about 1/8" below the seam on the back of the tank.

The second photo is the tools I used. The dust mask is a MUST HAVE and the Dremel with the rotary saw got the most use.

Not shown is eye protection because I am wearing it. If you do this, plastic bits will be flying all over.