A code 4 is just an advisory that your wiring (or whatever) does not comply with current regulations,there is a similar thing for gas as well.
Parksy, the quote of mine you used sums up exactly why pir`s need to be implemented as most vans do not comply with current regs(since 15th edition).
The actual testing is very straight forward and should take around an hour and a half. It is the finding and disconnecting that takes the time,most modern (2000 on) vans have plugs or connectors at appliances and i tend just to switch lights off. However there are little things like the LEDs in sockets that upset the insulation test and must be removed.
All of you that asked a sparky who told you he could do it in an hour, I bet you never told him he also had to play game of hunt the thimble before he started the test.
Therefore id like to set you all a challenge.
Time yourself and starting at the 240v consumer unit trace all the wiring to each circuit, find the appliance connector (do not disconnect). so you have the water heater,space heater,battery charger,fridge,lighting circuit,wiring to all sockets not just 3-pin (how many have LED's),possibly cooker,microwave and any extras.Allow an hour and a half for the testing itself then reassemble all covers/cushions that you have had to lift to find cables. Oh,i almost forgot, you need to trace the earth bonding throughout the caravan as well
Ill lay odds not one of you will do it yet still tell us we`re having a laugh when told the test will take 4 hrs