So after some investigation I found out that Alex is totally right there. They are diesel driven and the box is under the skirt or somewhere else on the frame and on the back there is just a little ventilator. I´ve tried to get dimensions of such a box but can´t find anything. Does anyone of you (any truckies around?) have the chance to get the measuring tape out and find out what the dimensions are??? I don´t come across those units here unfortunatelly
