Need advice re chance of damage to a stainless steel tray in a very hot oven
The temperature of boiling water is 100° Celsius or 212° Fahrenheit. This is considerably colder than the self-cleaning cycle in your oven. It would be perfectly sufficient to set the oven temperature to about 120°C/240°F to heat the tray. It would not take long to reach the desired temperature for the tray at those lower temperatures since metals conduct heat well.