Bikepacking - a viable alternative to racks & panniers

The seat tube bottle bosses are really high on that frame.

Could get a top tube bag and some fork leg bags if you needed some extra space.

have fun in the welsh bit. Hope weathers good for you.

if the route goes anywhere exciting in wales, you'll want a smaller chainring

Yeah, I'm thinking £25 rack and throw a tent and sleeping bag on the back.
Leave the seatbag for races.