Rafts must be used to get the right curvature on the bottom part of the surface. Infill dos not matter, it is a surface just increase shell thickness (>= 1.2mm). Supports: Touching buildplate only suffices. I've used a simple GNU/Octave script to generate the initial STL and OpenSCAD to rotate it to a good position for printing. Then added some thickness using Meshlab - http://meshlab.sourceforge.net/ (inflating the original STL file) using the filter Uniform Mesh Resampling and setting on the 'absolute distance' option and specifying a reasonable offset (1% ~ 2%) and a reasonable precision (0.2% ~ 0.5%). I encourage you to give a go on Meshlab to see how it goes. The best surface to print is actually printed was 10-roman-2.stl. The version 3 will also print nicely.