For your 240V-30A - 3 wire feed - the Spa Panel would be set up like this:
Your wiring plan could be this:
And - as always - Click on the image to see a full scale diagram that is printable on Tabloid paper (11" x 17")
BTW: I still do not see the need for a second temp probe. Keep in mind that when you are using the BOIL kettle, the PID would be in manual mode. Yes, it needs a temp probe connected - however the probe in the HLT would still be connected and not used. So: I'm puzzled with how you would be using a second probe.
I hope this helps you.