Chevrolet stove bolt engine truck shop manuals show/describe no gasket on either side of the insulator.
If I am incorrect, please post the year of the manual and the page(s).

However, most people use a gasket between insulator and carburetor (with appropriately placed "cut out" in the gasket). A gasket between insulator and manifold is usually not needed, but would cause no harm (unless it leaks).