I used a truck box with a 10 in it for my roadster. Works good, although the sub barely fits in the box, and its a little tight squeeze under the divider. It could stand to be wider and a bit shorter to physically fit underneath the divider better, but it was something I already had and fit when thrown in so I can't complain too bad.

As far as powering the amp. I ran a ground wire from the amp to the obvious 'frame rail' tube and connected it with an eye and a self tapping screw. I ran a new power wire theough the passenger compartment straight to the battery. For the remote turn on wire I connected it to my aftermarket head unit. If you are retaining the stock head unit then you can tap into the keyed power wire at the radio connector, but I can't imagine why you would keep the stock head unit to power a separate sub.

Pics of your box installed in the trunk would be good.