Auto Lock / Unlock

Here is my question. I had a DEI alram with remote start and keyless entry and when the car was started all the doors would like and when I turned it off all the doors unlock. I no longer havethis installed, instead I instead the Codealarm ad on remote start to the factory alarm (which works pretty good I may say).

The thing with this is the doors unlock when the car hits15 mpg, but when I turn the car off they do not lock all the doors. It also don't have a passive auto locking feature.

The QUESTION: Is there a way to hook up relays to the doom light and door locks to get this done? Or the ignition wire and door locks/unlock.

I have  a 2003 Chrysler PT Cruiser.

I want the doors to lock passively, I want them to unlock when I turn the car off.

Thanks for your help.