Have you tried using the list-table directive? I find it's a much easier way to create tables - it's based on writing indented lists which mirror the logical structure of the table (i.e., table / row / cell), rather than trying to produce ASCII art.
All my doc is in Sphinx so I play it safe, and all directives need to be supported in whatever version of docutils and rst2pdf are installed across the various developer machines. So for the moment I am stuck with ascii art.
