First make a surface by trimming all those curves with a plane so each is separate, then using the Interpcrv command and the Near object snap to create a grid where each new curve crosses each original one. Use the NetworkSrf command to create a single NURBS surface. Then offset that surface inside, so that you have an outer surface and an inner one. Split them with a plane to remove ragged edges, and split the plane with the surfaces to make a flat surface that connects the two face surfaces. Join all 3 surfaces to create a solid (as far as Rhino's concerned, anyway) and if you want to print it on an additive RP machine, save it as a STL file without open objects.
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