Per FAR 22.1003-1, the Service Contract Labor Standards (formerly Service Contract Act) applies to "...all Government contracts, the principal purpose of which is to furnish services in the United States through the use of service employees, except as exempted in 22.1003-3 and 22.1003-4." Regarding refurbishment of the flatbed trailer, I found no exemptions in either 22.1003-3 or -4 that appear to apply to trailer maintenance. As for regular vehicle maintenance, 22.1003-4(d)(1)(i) may provide an exemption, subject the conditions at 22.1003-4(d)(2) and (d)(5). Also review the requirement regarding "sole source" maintenance at 22.1003-4(d)(1)(iv) for both vehicle maintenance (and the flatbed trailer maintenance) . The various conditions and exceptions can be very challenging to follow, but it is ultimately the contracting officer's responsibility to confirm applicability of the SCLS after reviewing FAR 22.1003.