I don't know how well this will work with your manufactured house boat but
we used vinyl siding fascia panels for our houseboat's ceilings.
advantages: very light, attractive bead board look, no paint needed, easy to
install with narrow crown staples or brad nailer. This stuff comes in solid
or perforated panels about 8" X16'. It is easy to install over firing strips
about 2-3 feet apart.
However our house boat is pretty much like a stick built "land" house, just
built on a barge. Maybe you can do something with this idea.

--
Ron White
Boat building web address is
www.concentric.net/~knotreel