So the banana plugs on the back of my sub failed/the plastic back plate melted when I used the sub as a wind break. I decided to re-do the connection using really good Neutrik Speakon connectors.
These handle high current so are suitable for the job. The connectors are 4 pin, I used 2 pins of the connector per conductor (as in the photos below). The cables are wired so that the black cable goes to 1- and 2-, where red goes to 1+ and 2+. Wiring had to be done with precision and was quite surgical to avoid any shorts.