I am looking for a source for a one-piece enclosure for a complete
marine 'head' (otherwise known as a bathroom). That is, I am trying to
find a unit (probably fiberglass these days) which would fit aboard a
boat (we're doing a retrofit) and provide a complete
toilet/sink/shower combination in a tiny space. I've seen things like
this on many a boat, train and motorhome, so I know they can be done,
but I'd love to find a pre-made one rather than have to design and
build one myself.

I've been looking for the same thing with out any luck. However,
asbcorp.com sells shower walls and pplmotorhomes.com has sinks, etc.
4x8 fiberglass sheets are available at home depot. Please post if you
stumble into someone who manufactures them.

Thanks

There you go:

http://www.altor-industrie.fr/accueil.htm

Bingo! Flupke-ga, you are my hero! That's *exactly* what I've been
searching for, to no avail. Now that you've pointed the way, I'd
really appreciate it if you could tell me how to describe what I'm
looking for (I figure if these guys do it, someone else does as well,
but I still can't find 'em!) Thank you so much for the link!