others will sure join in with their solutions and advice... in the meantime...
I have hardwired power supplies for two cameras on my ship: Power is supplied from a separate 3A CB to a dedicated switch on the panel. From there one single power (20AWG) wire goes to the VS top fairing, whilst another wire runs thru the left wing to an angle screwed into the tie-down thread.
A small 12V/5V transformer, with its ground wire, is fitted at both locations, as the cameras rely on a 5V supply.
In practice I turn on the master switch, turn on the CAM labeled switch, individually start the cameras, turn the iPad on and establish the WLAN connection. One can then start the engine and go for a flight, whilst remote controlling the cameras to either film or pause. Some discipline is required, since any power interruption will require a manual restart of the cameras since I removed their batteries and they only rely on the ship's power.
Hope that helps