I very much doubt it will work, I've been on a 10A supply for years with a 10A in the van, should it overload it's always bypassed the vans mcb and trips the post or indeed in the case of an RCD, it's common to go back all the way to the main site isolation board and trip that.
Several reasons but mainly MCB's are built within tolerances, some then will be slightly more sensitive than others, also, the post MCB will have been abused more than your van and this generally weakens them and increases their sensitivity