Ok going with removable top box, it will be perfect fit as I'm glassing on top of existing pannel, it should release easy because of the blue release agent, leaving it overnight to go off.
Cut up a cheep Chinese led rear license plate indicator set up to get a light fir each side, cut about a 3rd out of PCB and got rid of plate illumination. Don't buy these for a bike as indicators are too close together to be read legal usa or uk.