We always leave the small double made up but take the bunk down even though it's a pain, I don't like the thought of it flying round the van if it comes loose.
In our last van they recommended that the van never travelled with the bunk up, and thinking about it there will be a lot of stresses on the couple of screws on the wall plate. Take it down to be safe.
Safer if you take bunks down, as it could cause your outfit to sway a bit. Hope you enjoy your trip to Wales , sorry to say it's raining here at the moment