Cal. Rev. & Tax. Code § 6282

There are exempted from the computation of the amount of the sales tax the gross receipts from sales of mobilehomes or commercial coaches required to be annually registered under the Health and Safety Code or vehicles required to be registered under the Vehicle Code when the retailer is other than a person licensed or certificated pursuant to the Health and Safety Code or the Vehicle Code as a manufacturer, remanufacturer, dealer, dismantler, or lessor-retailer, subject to Section 11615.5 of the Vehicle Code.

This exemption does not extend to the rentals payable under a lease of tangible personal property.