Paul, that's impressive! And I say that as an archaeologist...
Matt, no doubt the bath house and more important buildings might have some marble detailing inside (floors, columns, etc), but the site it is modelled on in Germany is just too far from the Med for transporting large amounts of marble. It's a big, heavy material to cart overland, so the cost would be staggering. The bulk of the shell would have been local materials, rendered and whitewashed to make it look more "Roman". Now, if there is to be any visible marble, it'd be on a temple or a triumphal arch...