Yes, after it was all setup, it would work similar to an Opus.
The Tank circuit is as simple as what I show above in the text diagram. Wire up +12 from the car through a diode such as the MBR4045CT (available from
www.digikey.com) to the +12 volts of a battery. Then wire the tank battery to an inverter. Wire all the grounds together and viola, a simple tank circuit that will allow you to survive crank and bass hits.
The diode prevents current from flowing from the tank battery to the car, and is rated at up to 40 amps. The diode I chose (MBR4045CT, inexpensive) has a low forward voltage drop, which means that it is efficient (without going into a great deal of detail...) Also, so you know how to wire it up, pins 1 and 3 connect to +12 from the car, and pin 2 connects to the tank battery. If pulling high amounts of current, a heat sink may be necessary on the diode. Digikey number HS229-ND would work, and it's inexpensive.
KyferEz