It's up to you to spend as much as you like and design accordingly.But its a different argument, whether you need 1 or 2 RCDs (or equivalent eg RCBO on certain circuits).
Its not up to me though (in general) - there's a lot of regulation now which requires RCDs, etc admittedly for new installations not just repairs to existing ones.
But it isn't, is it?Mine is that the cable between a house and a shed will possibly either be more vulnerable than other non-RCD protected ones, or to make them as safe, is costly.
Do you mean it isn't less safe, or it isn't costly? I'm saying its one or the other.