Johnnyrock70,
The insulators are thermal barriers to help keep heat out of the carburetors and help prevent percolation of the fuel.
The last Fenton dual setup I worked on had the insulators installed. Gaskets were used on both sides of the insulators, making sure the vacuum port in the base of the carburetor wasn't covered and had free access to manifold vacuum.
Some folks run the insulator naked on the manifold and gasket the joint between carb and insulator but I have never seen a 'no gasket' situation.
Stuart
