I am sorry but your understanding of motorhome construction is incorrect. Even an "A" class motorhome such as a Hymer is a conversion. The base vehicle manufacturer e.g. Ford, Fiat, Volkswagon, Mercedes etc, supply the engine and powertrain, to which the converter adds their own bodywork to varying extents. Frequently as is possible with your MH, a lowered chassis is added to the rear of the cab. A common example of this would be an "Alko" chassis.
The point that I was making is that a Fiat Ducato van or minibus would not require extended side indicators, but I am not sure about a pick-up truck body which may be wider.
So is your MH a Swift, Chausson, or other conversion? Perhaps searching under converters name would return more results?