When the modular home was installed on its site, presumably you obtained permits. Those permits would have specified a minimum depth,dimensions and construction (reinforcement and attachment) for the foundation and footers. The question is whether those specifications were indeed implemented by the contractor, and inspected/passed by the permit authority. The permit authority should also have inspected the finished grade. So.
1) Did you have permits?
2) Have you brought your concerns to the attention of the management level of the permit authority?
3) Did you rely on an engineering design or construction plan by the modular home manufacturer for the foundation and grade?
4) Was the plan implemented correctly?
4) Have you contacted an attorney, or why not?