Steve, not sure if fuses are re-wireable, they are the MCB type B (I think by comparason on Screwfix) if that has any meaning to this whole conversation. Also would need to rod in that case as in the van there is a seperate consumer unit, its just been tailed to a 16amp commando which then used to uplink into the carvan park power when it was sited.

So, ideally thinking logically let me think basic.
Say the carvan was designed to trip 20amp, then really it would be better if the house fuse was larger eg 30 amp, this way if the van tripped it wouldnt trip the house. (Hoping my thinking is right here)

30 Amp, will need a 6mm Core - Check,
Earth Stake - Check,

If having its own Earth rod then, does the 3rd core come into account?