While it is not "illegal" to have more than one insurance policy on a vehicle, the vast majority of insurance companies have problems with it, because of the possibility of “unjust enrichment” if you get into an accident. Unjust enrichment means that you should be unable to profit from a loss on your vehicle. In theory, you could file two claims on a wreck and possibly get a double payout if both companies pay, in otherwords, paying twice what the actual damages are. With that being said, if you were to file claims agains both companies for the same accident without notifying them of the other coverage, this could be construed as fraud and and you could be subjected to various fines or penalties. As long as you make sure you notify the companies of dual coverage, that should cover your responsibility. If there were to be a claim filed, I would (again) remind them of the dual coverage. Please let me know if I can help further.