I always thought the area just below the 'change tray' (top/center of dash) and just above the 'face' vents would be a good spot. room for at least 4.
This is the spot I will use when I get around to adding more gauges. Good visibility but not 100% sure on the wire routing.
There is a plug on the inside cowl on both the driver/pass side visible when the hood is up, this is where I run my extra wires from eng. bay to cab.
Good luck!
Pad