Can you bypass that control box to get constant 12V from the battery? If you unplug that connector labeled "POWER", is it a constant 12V? I bet one of those other two goes to the plug in the ceiling. You could just cut that box out of the equation. The upfitter connection in the passenger B pillar is a direct 12V from the battery with a 70A fuse on it. It's constant, so any timing mumbo jumbo is in that box.
I also have those puck lights (I'm sure about half of us do), and I have mine on a simple rotary dimmer.
It's pricey, but it's also nice and small.