I'm an amateur radio operator, and I operate a dual-band VHF/UHF transceiver in my '03 Corolla LE. I tap the power directly from the battery terminals. However, my radio requires a solid 8 to 10 amps while transmitting at full power, and the current directly from the battery is less likely to have any sort of impulse noise, since the battery acts like a large filter capacitor. This also provides a more direct and reliable DC ground for the radio. Of course, the power source to the transceiver is always "on," and the transceiver will work whether the car is switched "on" or not. The transceiver has an automatic power off feature which I have set for 2 hours of play time before the rig goes to sleep.
For your purposes, I should think that a spare fuse location on one of the inside fuse blocks would suffice. Be sure to use large enough wire to carry the maximum amount of current required, 12 awg. stranded wire will probably be way more than adequate, but if the radio only draws an amp or two, you could get away with wire as light as 18 ga. Red/black colored "zip" cord would be ideal. Be sure to attach the ground firmly to a good ground point, preferably one with a direct path back to the negative battery terminal. BOTH positive and negative leads should be individually fused. Naturally, if you're tapping a fuse block, you already have a fuse on your positive, or "hot" lead. Just be sure to fuse the negative or ground lead as well. This way, if the main ground lead to the battery should fail for any reason, your new radio won't be subjected to the surge of starting current trying to find a path to ground through your radio. You'd pop the fuse, not the radio.
