Trailer Coverage under BAP

In the opinion of FC&S, and in consideration of the form CA 00 01 10 01, business auto coverage form, does provision c—certain trailers, mobile equipment and temporary substitute autos—apply to a loss if the insured has symbol 1 for liability coverage?

In other words, we have an insured whose unscheduled trailer, with a load capacity of 2,000  pounds or greater, was involved in an at-fault accident. Do you think provision c. 1 prohibits liability coverage to this unscheduled trailer?