California Code, Revenue and Taxation Code - RTC § 10753.4

(a) Notwithstanding any other provisions of law, every dealer who sells a trailer coach required to be moved under permit shall state on a certificate attached to the sales contract the cost price upon which the vehicle license fee is computed separately from the cost of accessories or other charges for such trailer coach.

(b) The department shall determine what items shall be included and what items shall not be included in the cost price upon which the vehicle license fee is computed for a trailer coach required to be moved under a permit and the manner of computation of such cost price. The department shall notify every dealer authorized to sell a trailer coach required to be moved under a permit of (1) the requirement that the sales contract state the cost price upon which the vehicle license fee is computed separately from the cost of accessories or other charges for such trailer coaches and (2) the manner in which such cost price is to be determined.