I just use a carbide hole saw, then mount with couplers, o rings, and ss nuts. I then use high temp, food grade silicone caulk to seal it, works pretty well.
I know a lot of people use temp controllers with SSRs, but that's still on/off so I am afraid it would still have issues. At least with an SCR I could control the voltage to my heating element which should decrease power. I already own a $20 one but I was hesitant to use it because that's a lot of power running through a dinky thing. Also I can only get down to 120vac and up to 230vac, so I dunno if 120 is low enough to keep it safe. I guess I could get two SCRs, one for each hot leg, then just tweak both knobs back and forth, don't know how thatd turn out. How do you do it, sneezles?
If I use a SCR, do you think I still need to circulate the wort around as well?