Should be under bonnet n/s/f against bulkhead on RHD like normal diesels, but I did have one Renault based camper that it was in the top of the fuel tank like a lot of modern petrol engines and had to drop the fuel tank due to the conversion covering the access hole.
Can you not trace back down the fuel line from the high pressure pump on the engine?
See item (2) in diagram following "INTRODUCTION" in this link.
The fuel filter may be either a metal canister type, or a so called "green" filter of UFI manufacture. The UFI filter on my 2006 2.8JTD is all black, so could be difficult to see through the letter box like slit of an A class MH. The references to a green filter in eLearn when referring to the UFI filter can be confusing.
I believe there is no separate water trap, it's all part of the fuel filter assembly which has a "water in fuel" sensor in the bottom. There is also a drain screw and outlet, see pic for a typical arrangement.