Has anyone figured out a way to get a 12 volt power source to be hot when the truck is off ?

 

How about a dedicated 12 ga. wire directly from the + side of one of the batteries to where you need it. Wouldn't hurt to install an inline fuse with the right amps needed to protect your system. Obviously you'll need a ground wire somewhere.

 

Check for an unused Fuze slot that stays hot,
with the ignition off.

 

Just remember if you connect anything directly to the battery on these new trucks you are bypassing the Battery Monitor System. And by doing so making the alternator work less loaded, and likely keeping your battery at a lower charge level than it optimally needs. All load demand is monitored by the PCM, which tells the alternator how much to generate. Same goes for connecting grounds directly to the battery.