The newest devices (evidently) allow you to individually enable/custom maps but the older ones don't. For example, my Montana 600 is "all or nothing" just like your Dakota. I don't think there's anyway around this, or at least I've never seen it after all these years.
The sad fact is, Garmin intentionally crippled the custom map (.kmz) format. Apparently they were concerned it would be too much competition for thier own products. Their Birdseye products use the .jnx format that supports multiple maps of almost unlimited size for example.
I've never tried myself, but evidently there are ways to make your own .jnx maps. This forum has decided it isn't appropriate for discussion, but Google might give you some ideas.
