In National Indemnity Co. v. Manley (1975) 53 Cal.App.3d 126, the appellant asserted that the requirement in an indorsement to the policy that trailers be rented only to persons having automobile liability insurance constituted an underlying insurance requirement in the policy satisfying subdivision (a) of section 11580.1. Ultimately the court rejected the contention because it concluded under the statutes then in effect that such insurance obtained by the lessee would not constitute primary or underlying insurance. However, as to the "requirement" aspect of the problem, the court said: "On its face, this provision of the special endorsement appears to require underlying insurance coverage." (53 Cal.App.3d at p. 131.) However, the indorsement relied on by the appellant in the National Indemnity case was altogether different than that relied on by Premier in the case at bench. The indorsement in that case provided: "'It is understood and agreed that it is warranted by the named insured that trailers rented to others will be rented only to persons having automobile liability insurance which will be in force for the term of rental.'" ( Id., at p. 129.)