Am away in Spain at the moment and my black box charger, located under the R n R bed on my 1990 Westy Atlantic, is getting seriously hot when I've connected the hook-up. Its obviously charging both main and leisure batteries but should it really get so hot. I have the fridge running on 220/240 volts as well, though its struggling in the 30C + temperatures.
I've been on several European trips in mine and you kinda get to know it's foybles....the BBB (buzzing black box) in my California also can get very hot at times, it does cool down after a few hours of charging, I guess after the batteries have topped up, even then it remains warm.
Obviously make sure the immediate area around the charger is clear so it has some air circulation.
I must admit to being slightly concerned myself but i've spoken to enough owners to realise this is normal.
I guess if this really does bother you an idea could be to set a blow fan (on cold) under the seat.