Skins disappear when overriding Render method

[John]

I'm trying to override the page's render method, and capture the result for
processing, eg:

protected override void Render(HtmlText Writer writer)
{
//base.Render(wri ter);
StringBuilder renderedOutput = new StringBuilder() ;
using (StringWriter strWriter = new StringWriter(re nderedOutput))
{
using (HtmlTextWriter tWriter = new HtmlTextWriter( strWriter))
{
base.Render(tWr iter);
}
}

// save renderedOutput. ToString() to a file
}

This works great, but my page theme (specifically gridview skins) arn't
applied! If I replace the call to base.Render() they work fine - does this
mean skins / themes arn't rendered in Render()???

Thanks,

John