If by "random stop" you mean a stop justified by any one of the hundreds of sections in the motor vehicle code, the answer is yes, you generally need a warrant. But there are lots and lots of exceptions to the warrant requirement for a moving premises.
Two of the most common ones are:
1) Consent. The driver says, "Yea, go ahead and search." Lots of arrests for contraband follow those words.
2) Search incident to arrest. Arrest the driver for minor charge (no ops, no insurance, unpaid ticket, whatever), and a complete inventory search is standard procedure.
You talkin from experience Mr.??