Motor mover isolator

Interesting as on our Pegasus iv it was already wired for a motor mover,when built and the isolator and control box in the outside locker so it may mean moving control box as well, our leisure batt is fitted under the centre of the van  

That sounds like a cop out to me, njh. There’s no need to have the isolator switch by the control box. In fact many people think the closer the isolator switch is to the battery, the better.

Every van we had with a mover had the control box under a front bunk and the switch in the battery compartment.

In our previous U3 Barcelona - which is essentially the same layout as your Valencia, the control boxes were under the bed near the wheel arch and the isolator was mounted on a panel just inside the locker, so that I could access it from outside by opening the locker door. I asked the dealer to do that when fitting the MM and it wasn't a problem.

On our current van - Knaus Starclass - the isolator is mounted in the battery box, directly underneath the 240v socket - so that it's impossible to accidentally switch on the MM whilst 240v power is connected.

When the motor mover was fitted to my u3 Valencia, they fitted the the control to the floor under the bed and the isolator through the end of the bed in the gap between the fridge. It was a real pain having to get in and out to turn it on and off. 

I refitted the control box up of the floor to the inner bed side - freed up floor space and removed the possibility of it getting damaged should anything slide when travelling. As for the isolator I installed an additional one in the outside box under the 13pin socket just moving the sat connector slightly to the side. Leaving the existing isolator in place I extended the wiring to the new switch, connecting it in series. Works just fine. Saves opening the door unnecessarily, especially if it’s raining. The inner one I only use when the caravan is not n use, just turn it on before a trip then off when back home.

The extra distance of the cable run won’t be a problem as long as you use the correct size cable. I think the fitters may get confused about the cable length causing problems because the instructions state that the cables to the movers from the control box must be the same length as unequal cable runs can make the motors run a slightly different speeds.

The unequal cables to the motors is where the information about voltage drop would have come from

I keep thinking of doing what njh suggests but that's as far as I get. My mover's isolator is also under a front locker & is  PITA to get to and as the mover will auto switch off it means I've to maul about entering the caravan any such time I want to use the mover. Hence I use the tow car most of the time.