The NCC ( National Caravan Council) where promoting the PIR a few years ago as becoming part of the requirement for electric hook up on sites and all members of the Approved Workshop Scheme (AWS) had to train up to provide the PIR.
As far as I am aware the sites never took this on board and most people have ignored it. If you have your motorhome serviced by an AWS member you should be offered a PIR as an extra to the service from my knowledge I would suggest you contact an electrician as the methods taught by CITO who train the AWS members is not the ideal way of doing it and can be quite costly due to the strip down of the interior they require
I only know of one member (a mate of mine) of the AWS who is properly equipped and had the benefit of some extra training from me who can do it without taking the motorhome / caravan apart
For information the item that fails most is the hook up lead from low insulation resistance my mate has had them as low as 0.2MΩ
As previously stated you should have a PIR / EICR as to whether you will be asked to produce for hook up is a different matter but I would recommend using an electrician
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