A martian colony has little economic incentive to it. A lunar colony on the other hand is a potentially profitable enterprise since lunar materials could be used to make satellites for earth. The surface of the moon is covered in Oxygen (useful for filling habitats), Iron (useful for building habitats and good for export) and silicon (useful for export, aka solar panels for powering satellites or even for sending power back to earth via microwave transmission). And the atmosphere on mars is hardly an asset as it is far thinner then earths and will cause erosion, unlike lunar vacuum. The only reason to send a mission to mars is to investigate the geology, while a mission to the moon could be a permanent settlement with a strong economy. And that's not even getting into the benefits of a six round trip over a three year round trip or the fact that getting anything back from mars would be nigh on impossible.
Therefore I recommend building your fortress on the moon not mars.
Also, plastic would be difficult to produce on either the moon or on mars as neither planet has the petrochemicals we make plastics from. Maybe plastics could be an import good?