What I've seen over the years, is that it doesn't matter what gasket you use, what sealer you use, how much you torque it down, smallblock mopar thermostat housings always leak
I too have not had good luck with any manufacturer thermostat housing sealing, but I have to say that the silicone gasket I referenced above has not leaked a drop in 2 years, uses no sealer, and is reusable.
The housing was new but the manifold was all pocked up from 51 years of use
