While my box is not in the car, I use the AC-DC power adapter that came with the case (morex cubid 2677R) which provides +12V DC:
I replaced the existing female power plug and wiring with a new plug wired to the Opus. I then added another female power plug for the remote turn-on signal. I added an SPST switch with a diode to override the remote turn-on signal. When I bring the box inside, I simply connect it to the AC-DC power adapter and flip the switch.
Code:
O +12V O head unit .----------.
| | | DC-PS |
| --- | |
| \ / | |
| --- | |
| | | |
| | | |
| o--------------o Remote |
| | | Turn-on |
| \ switch | |
| \ SPST | |
| | | |
| | | |
'---------------o--------------o Vin |
| |
| |
'----------'