Those AMP connectors are UL Listed to be installed without a box; but they still need to be accessible.
That is not really true
They come under 545.13
545.13 Component Interconnections. Fittings and connectors
that are intended to be concealed at the time of on-site
assembly, where tested, identified, and listed to applicable
standards, shall be permitted for on-site interconnection of
modules or other building components. Such fittings and connectors
shall be equal to the wiring method employed in insulation,
temperature rise, and fault-current withstand and shall
be capable of enduring the vibration and minor relative motions
occurring in the components of manufactured buildings
The installation instructions say
B. Building Site and Dwelling Site
The separate modules of a building or
dwelling assembled on location are to
be connected elec
trically by the
simple plug-in connection (including a mechanical latch)
of mating pairs thereby providing circuit continuity.
The connected pairs may or may not be fastened in
place. The connected pairs may or may not be
concealed by the installation
