I have no cracks on my dash of my new 300D and want to keep it that way. What exactly is it made of? Should I use a leather conditioner or vinyl? Thanks

Considering its vinyl I would use a vinyl product. I use Aerospace 303 as it has high uv protection and I like the product.
For what its worth Leatherique recommends using petroleum jelly. Wipe it on, let it soak in under the hot sun and then wipe and buff. Sounds like a good recipe for a shiny dash reflecting onto the windshield.