JohnD said:What is the brand and age of your RCD (and consumer unit)??
And can you see what other numbers are markings are on it please?
I might be about to suggest something...
BTW do you have an overhead or an underground supply? About how old do you think the supply cables are? is there an earth spike?
You might as well unplug the freezers when you go to bed. they should withstand several hours with the doors shut... and you're expecting a power cut during the night it would be a pity if we didn't track down a fault to one of them. If you have one of those 30mA RCD adaptors used for lawnmowers, perhaps you could connect things through that and see if it trips? the 100mA trip is quite a big one.