Here's my PID project, completed about 2 years ago.
Box is from Marlin P. Jones Co. Heat sinc also.
Thermocouple goes right in the bottom, It's a non sealed unit,(type K), that I have screwed into a ¼" connector that's screwed onto a ¼ bolt with copper washers above and below the bolt.
I've up-dated the project with a connector/plug like cranium has for the thermocouple. I have both 20# pots,(one is bottom pour, the other is a melter), with their own TC that I can unplug to change pots. I also put a female plug socket for the plug from the pot. I have 2 more pots to get rigged for the PID. One is an old saeco melter that has NO T-stat.. The other is a small lee melter that I may just leave be.
I really like the ability to move the PID from one pot to another. But a word of warning, it takes a while for the PID to re-learn the different TC from one pot to the next. Both pots are the same wattage as well as the TC's It settles in after an hour of running, even then, it beats the he!! out of the lee T-stat!
Cranium, I'd definitely get that SSR out of the lee enclosure. It will be running too hot where it is. I certainly didn't need that big heat sinc for mine, especially because my SSR is a 40 amp!
When wiring the power side of the SSR, just un-plug/remove the jumper from the lee T-stat, then plug the other wire that went to the lee T-stat to the heater element. The, IF you ever want to make it work on more than one pot, get a wall plug from the hardware store, wire that into the power side of the SSR. then simply plug the pot plug into it.
I'll post this now, then go take some more current pics of it, should make the explanation easier.