i would just stick with the battery, i am putting mine in tom the pos. is going on the battery but i the ground is just going to the frame its to far away to run a ground IMO. Where do you want to mount yours that would make the batt not an option?
i'm mounting on top of the windshield washer tank so it will actually be right near the battery but i was just curious as to other options. maybe somewhere to keep the wires out of sight.
I ran my positive wire to the terminal on the fuse block and the negative to a starter bolt. My battery is in the trunk so I only had to run 4 feet of wire rather than 8.
Ran mine to the fuse block as well. I put my box on top of windshield fluid tank (which now my overflow tank) and my fuse box is in the fender right below it. Then I just ran the ground to the frame.
Battery is probably the best place, but I connected mine to the power wire on the alternator. I mounted the ignition box in the glove box so I grounded it to a bolt behind the glove box.
i am sure there are other places you could get power, but battery is probably the easiest and makes the most sense considering most people mount the ignition under the hood...
Battery is your best bet really. It doesn't drain your batt, as it doesn't come on until it gets signal from the coil wire anyway.
For stuff that needs to come on with ignition power under the hood, I wire them to the fuse terminal designated for the Convertible top (since it is unused in my hardtop )