He needs to contact any commercial insurance broker and tell them he needs the following:
minimum of $750,000 Auto liability coverage for ICC cert / DOT cert
Commercial Cargo policy set in the limits of the value of the boats that he will be hauling. If he will be hauling high dollar offshore boats he needs a minimum of $500,000 in coverage.
Unless he has prior truck commercial insurance he may pay a steep premium for his policy. Good luck
He also needs to apply for both a ICC certificate and a DOT number.