I don't think you would need the OPUS 150-watt for that setup you described abode. I would suggest you look at the OPUS 90-watt it's a lot smaller then the 150 watt and it would be ideal for your setup. It might fit in your case.
Alternatively, the PW-70a doesnít regulate the 12 volt rail (I'm not sure about the PW-80). You would sell need some sort of startup/shutdown controller such as the ITPS, with the voltage regulation option disabled.