Further manufacturing of used chassis previously subject to FET

We want to add a piece of equipment (not a body) to a used truck chassis. The used chassis is older than six months and was taxable under Internal Revenue Code (IRC) Section 4051 Federal Excise Tax (FET) when new. The cost of the equipment and its installation is not expensive. Is it correct that the addition of the equipment will not constitute further manufacturing (and will not trigger new FET)?