In message , Christian
McArdle writes
The normal way to put sockets in plasterboard is to use dry-lining
boxes, I think these would eb the best way for the OP's situation
too rather than using metal boxes fixed on the wall behind the
plasterboard.

OTOH, metal boxes do have some advantages.

1. Much firmer, good for knocking in stiff plugs.
2. You don't get that white lip, which can be obvious is differently shaped
to the socket, or the socket isn't white.

Indeed, which is why I prefer to use them if possible in most
situations.
--
Chris French, Leeds