Another suggestion would be a D slot pin in a slot with a clamp on the outside to hold it in, if you decide to drill right through and pin/bolt don't...
Hi Steve maybe if you make a grove/channel through the tube into the rod inside and use a pinch clamp with the bolt securing the components together...
Couldn't do without those pads so useful, I don't envy you with the wiring, something I've got to tackle in the near future, there's just so much of...