Tips To Getting T-stat Housing To Seal?

I just replaced mine a few weeks ago, no leaks, used the normal felpro gasket, no rtv. I take a piece of fishing line and run it through the part of the thermostat that sits in the housing. I then tie it together so its a circle and run it through the housing where the hose to the radiator goes. I put a screwdriver through the fishing line, and twist it till the pressure is holding the thermostat in place, put the gasket on the housing and slide the bolts through. Line it up with the engine, and then tighten the bolts up. Once its all tight, I untwist the screwdriver and cut the fishing line, pulling the line out as one piece. This prevents the thermostat from sliding around during install. I have done it twice now and both times no issues. I got the idea from another member here who used a rubber band, I just didn't have a rubber band available.

Black RTV again for the win. A thin bead to both sides of the gasket and then I let it set for a few hours before I even think about running fluid through it.

And brake cleaner first to clean everything before applying the RTV, on both sides of the gasket.