Unfortunately there may be several issues here.
Right to start, you said "tiny shocks". Is it a mains type shock or a static electric shock? A mains fault one will happen everytime you touch the van when hooked-up, a static one will happen once but once discharged you should be able to touch the bodywork without receiving a second one and will happen regardless of being hooked-up. (That may seem obvious but best get the obvious out of the way to start).
Is this the first time ever you have used the hook-up?
The thing to understand about RCD's (the sensitive 'trip switches') is that they will only 'trip' under certain conditions;
1. The fault current must have a path to earth (and it's not fussed whether that's via a copper cable or via you) AND
2. The fault current must be above a certain magnitude (30mA is the usual setting)
What I
suspect is happening here is that you do indeed have a fault which is finding it's way onto your bodywork but is not sufficiently bad to exceed the RCD's 30mA setting so the shock you are receiving might be say, 25mA. If it were greater than 30mA, both the RCD in your van
and the RCD at the hook-up point should 'trip' (unlikely, but not impossible that they could both be faulty). The thing to understand here is that they should trip regardless of whether the vans earthing or the hook-up earthing (or both) is knackered; you have become the 'earth' as soon as you touch the van.
There are
lots of other considerations here; your vans hook-up earthing, the campsite's hook-up earthing, whether your bodywork is connected to the van hook-up earth or not etc but for now I would suggest the following:
Get an
electrician to swap the 16A blue hook up plug on your hook-up lead for a 13A plugtop and test that the lead is without fault. Plug it into the household socket circuit (which should be on it's own 30mA RCD by the way). Without touching the van metalwork jump in through the sliding door and switch the hook-up main RCD switch into the 'on' position. Press the 'Test' button on the RCD and it should 'trip'. If it doesn't it's knacked. Jump out (mind the metalwork!!) and unplug the hook-up. Get the electrician to carry out a FULL test and inspection of the van hook-up and internal wiring. If this proves fault free and hunky-dorey, he might as well issue you with a certificate saying so while he's there. The only other way of getting a fault on the van is via the mains equipment in the van such as the mains side of the fridge so get him to 'PAT' test any mains equipment in there. If these pass aswell then the only other option is that the campsite hook-up was at fault and you should be able to plug your hook up back into the household socket, switch your hook-up on, switch the mains equipment in the van on and................touch the bodywork
You may find that the household sockets RCD 'trips' the moment you hook-up in which case go straight to the test and inspection part.
) so i corrected it and think that should have sorted it seams the one withg the standard plug worked fine!! 
thanks 1664