The NexStar 8 GPS and 11 GPS have a handy connector on the control panel to provide 12 volts to small accessories. The connector is just like the power cord connector on the bottom of the base - a barrel connector with outside diameter of 5.5mm and inside diameter of 2.1mm. Positive voltage is on the inside conductor, negative on the outside.
The manual makes no mention of the maximum current (amperage) that can be drawn through the connector. Celestron Tech Support generally states no more than 1 amp should be pulled via this socket but it is worth noting that the AC adapter is rated at 1.5 amp and the scope itself is said to pull .75 amp (750ma). From that, the general consensus is a suggestion not to exceed 750ma. Personally, I would never attach any device rated higher than 500ma.
This rules out all dew heater strips! You would find that some digital and CCD cameras would work at a low enough power rating as well as any electric focus motors that run on 12 volts. Nonetheless, be careful and insure you are not drawing more than 750ma total current. Drawing too much power through this socket will burn-out either the internal wiring or the slip-ring that allows the power to be plugged into the stationary base. Repair of such damage would be very expensive.