Is FET due on the resale of a tax-paid trailer within the first six months?

We are a distributor that just bought a taxable trailer from a manufacturer on a tax-paid basis. (We did not provide the manufacturer with a resale certificate, and the manufacturer’s invoice included the amount of FET under Section 4051 that the manufacturer would pay to the Internal Revenue Service.) We now intend to resell the trailer. A friend has advised us that if we re-sell the trailer within six months, we will have to pay Section 4051 tax on it. Is this true? I thought the six-month rule applied only to parts and accessories, and that Section 4051 tax was triggered only on an article’s first taxable sale.