Our fridge is only about 50ltrs because of the size of our van, and is of the Electrolux brand. So the settings on the dial to achieve the same temperature in two different brands and even sizes of fridges could be different. At this time of the year we find our fridge to run efficiently on No. 5, but I usually ensure that the left hand side of the van that the fridge is on, is away from the hot afternoon sun. This means that the fridge doesn't have to work so hard as it is a little cooler around the vents. We have no additional fans to assist the fridge ventilation. We generally, when choosing a site to park up on, would have the outdoor living side of the van (left side) away from the afternoon sun to gain extra shade so that both we and the fridge benefit. We are fortunate that the fridge is on the same side. Maybe worth taking into consideration for those planning their own motorhome layout. Keep the fridge on the on the cool side, perhaps on the side of the extendable awning.
Trusting these comments may be of help.
NZMCA No. 6244. Traillite Motorhome on Mercedes Sprinter 518 CDI.