Yes the traces are pretty light for those kinds of currents, and I did have some concerns on the track spacing around the SCR and the screw terminals. The fatter tracks use a spacing for 240v that I looked up online.
Humidity here isn’t “tropical” as such, the board will probably get a coat of lacquer anyway.
The circulating pump is rated at 240v/20 watts (so not much current when it’s running steady state), and the SCR I’m using is good for a few amps of continuous current draw with a fairly high surge current. The SCR has minimal heatsinking so it will go first in extended high current situations, there’s going to be a panel mount fuse before all of this that I’ll probably set to 2 amps or so.
The zero-crossing SCR controller I’m using “should” prevent switching on the pump at the peaks of the mains cycle so max current should just be the initial stall current from the motor before it gets up to speed.
The pump is an induction motor so the only concern I’ve got is false triggering of the SCR and being unable to turn the pump off once triggered. I used an example snubber circuit from the data sheet of the zero crossing controller and of course they said “your milage may vary”.