I've spoken to other older darkroom workers about fiberglassed sinks.
They always said that they had to do maintenance to the sink at some
point, like re-applying resin, etc, because either the sink started
leaking or the cloth started separating from the wood.

I took this information to heart as I built my own first sink.
Instead of using Fiberglass, I used a product called 'Gluvit' which is
a marine epoxy. I purchased it at a marine supply store - I don't
think you can find it anywhere else. I don't remember how I came upon
this product, but it has served me well. The current sink I am using
now was built about 5 years ago. No leaks at all. And for the past 2
and half years, it's been getting very regular use by the people who
rent my darkroom.

When I coated the sink, I just went for a natural look, mainly because
I didn't know any better. I think the next one I might build (if the
current one ever does leak) would be to mix gray paint into the epoxy
or paint it gray first and then epoxy over it.

One thing I would do differently would be to use a plastic or pvc
drain fixture. The metal one I installed is rusting.

Hope this helps.

dp

Don't know about sinks, but do know a bit about boats.  Epoxy/glass over wood
is a standard do-it-yourself boat construction technique.

The epoxy is applied to bare wood using a thin penetrating formulation.
No need to paint afterwards, unless you want a boot stripe or to paint
your sink's name on the transom^H^H^Hsplashboard.

Lots of information on the boat building sites.  The 'standard' epoxy
is "West", their site has tons of info/tutorials/etc.:

http://www.westsystem.com/