Just a small tip if you don't mind.
If I were you I'd put them on some metal or something. if you get a short-circuit or something there is a big risk of fire.
Straight on concrete .. metal trays do not help.
I dont get it, why metal trays doesn't help? They don't burn right?
Next time I am over, think I might just put them on a kitchen worktop. Leave the foam in place just worktop over it.