CG - First, let me welcome you to RCU!

I get rid of the gasket and put a small amount of RTV on the muffler flange and that works well. When using the gasket, it has a tendency to expand and compress causing the nuts to vibrate loose. Just toss the gasket. Another trick is to re-tighten the muffler screws/nuts after the engine has been run and is still warm.

Best of luck with this great hobby!!