I've fixed my Power Box in the right glove box and can lock it when open or remove the "prop" and lock it closed.
I used a steel tent peg bent to suit and covered with rubber tube.
Thanks to @Ambalana I bought a Crazy Mount 42mm on eBay. The adhesive worked on the glove box lid but wouldn't hold on the PB, so I bonded a steel washer to the PB, slightly offset to counter the weight of the cable.
Its been tested over 100 miles on rural roads and it stays in place. Simples!