One of the three spacehab modules to be landed on the Moon provides sufficient structure for attachment points and launch restraints for all the equipment the crew needs. The other two are in the pattern primarily to provide internal volume. We have the crew riding down to the moon in the Ascent Stage, mounted to the side of the Descent Stage propulsion package. The
Lunar Transfer Vehicle presumably provides sufficient space for a comfortable flight between Earth and Luna -- it has
to, because on the way back, it's all the crew will have -- so we don't need additional volume for the spaceborne part of the mission.
This allows us to consider an inflatable structure to provide the added volume on the moon. We could use one Spacehab with all its attach points and equipment, with an inflatable attached.
I don't recommend dumping the baseline design until we know a lot more about
this option, but we need to put it on the list of possibilities. Nobody
has yet identified a show-stopper other than the spectre of development
costs; and development costs might be simpler for an inflatable than for a
hard shell structure with all its fiddly bits.