1/700 scale ships bases

I would recommend the water base that is described in an article in the Nov 04 issue of FSM called "making waves".  It's done with a sheet of aluminum foil and Mod Podge.  It's easy, very inexpensive, and very realistic!  I can fax or email the article if you need it.  Just leave a no.

Not wood - that limits the search.

Go to your local Lowes/Home Depot and head to the back of the lighting department.  Look for the plastic diffuser sheets that go in the overhead fluorescent light fixtures.  They are 2x4 foot sheets.  There is a "broken ice" format which looks like a choppy sea.    The problem will be that the ship will sit on top of the chop instead of in the water.   You may have to inlet the hull into the plastic for better appearance.