You can do this with a 5$ parts store relay, or get a nice compact relay from an electronics store (or Amazon..)
Keep in mind that while power will ONLY be supplied when ignition is off (as requested), power WILL BE SUPPLIED when key is in accessory position.
Key in OFF or ACC = Device Powered
Key in Run and Start = Device Off
You can pull Ign1 power, and Battery power from the fuse panel...Get your meter or test light out...
Just make sure its IGN1 and not IGN2, as IGN2 will bounce on, off then on again when truck is cranked.