I marked a rectangle approx. 20mm in from left hand side and 12 mm down from the top.
The tool of choice is a drill attaching nibbler or hand nibbler to cut out a rectangular hole 25mm x 32mm in size.
Clean up with mild file and the chassis mount and it will fit nicely.
Use 45A Anderson crimp connectors for full current draw with suitable cable.
Altronics have an Auto cable W4158 that will do nicely. See Cable assembly pics.