My follow-up question would be: "How heavy is the glass cloth you're covering?"

Using 4-6 oz glass it should take 3, maybe 4, rolled-on coats to fill the weave enough to sand to a smooth surface without cutting into the cloth. Sometimes the waeve will be slightly visable even after the surface is smooth

You might experiment to see if you can apply a thicker coat by roller without getting runs.

Some people squeegee (sp?) epoxy on. I haven't tried this technique, but I think it might be effective for filling the weave without building up too much thickness.