I am not sure any of you guys consider this route for power supply.
- Get one of those cheap unregulated 12V PW series.
- DIY your own 12V rail from the Mastero/Sproggy (MK4+).
Combine the 2 now you have an almost perfect PSU.
Feed unregulated car 12V to the cheap PW PSU. Do not use the output from the PSU, instead use the output from the Sproggy.

The 12V MK4+ can be build without the hard to get MAX chips. National chip is easier to get.

Just a thought.