The blue Fel-Pro molded plastic gasket is kinda ugly; a better solution is the GM #10105135 gasket, with the same moilded silicone rings on both sides - it seals without having to use any goo or RTV, and as-installed looks exactly like the original paper gasket.
Important side note; John mentioned using 220-grit sand paper laid out on a perfectly flat surface like glass, and sanding the base of the T-Stat housing until the entire surface was smooth. This combined with the GM #10105135 gasket gave me the results I was hoping for. All you see is the gasket & no hint of silicone oozing out anywhere.
Thanks again John