The AC SSR's I use for controlling nichrome heaters drop around 0.6V across the switched terminals when conducting. They are spec'ed at around 1.6V drop, but in my applications I only see around 0.6V.

When dealing with mains voltages this is not a big deal. I will be curious to know what kind of voltage drop you see across your SSR? The relay, although a little noisy, at least does not drop much voltage when it is switching.

In AC heater circuits I have seen far more SSRs fail in a shorted condition than an open condition. It would be a lot better if they failed open, but Murphy's Law is at work, I guess.

Jim