Abstract: A mobile apparatus having utility in the construction of roof trusses at a job site. An elongate trailer frame is mounted to a wheel and axle assembly and is transportable on public highways by towing. A jig assembly supported by the frame is formed primary of uni-strut members and has a first elongate fixed position side rail and a second parallel but movable jig support rail. Plural transversely disposed jig members are slidably mounted for lateral movement along the extent of the first and second side rails of the jig assembly. A clinching device is mounted for longitudinal movement along the extent of the jig assembly by an overhead cantilevered track support structure. The jig assembly is longitudinally extendable, and the overhead track support member has a hingedly mounted auxiliary portion that may be deployed so that the clincher device can reach even the extended portion of the jig assembly.