This paper reports on our methodology and experience from a multi-year effort to cross-validate a vehicular network experiment with four hundred Dedicated Short Range Communications IEEE 802.11p transmitters through ns-3 simulations. With most of these transmitters in communication range, this represents an extremely dense wireless configuration that challenges radio and interference models. Field test and simulations were conducted in tandem and iteratively to facilitate model selection and configuration as well as to allow a detailed evaluation of simulation accuracy. We have learned that (1) results were most sensitive to parameter choices in the propagation and receiver models, with simulator default parameters not providing a good match; (2) results could, however, be significantly improved by adapting, implementing, and calibrating the propagation models and receiver models from the literature, yielding 88% accuracy (in terms of packet error rate compared to the field test) in such a complex large-scale setting; (3) the process was helpful in identifying errors both in the simulation models and in the experimental code and points to opportunities for further research.