Sealing timber frame wall onto rendered wall

[Hastings]

What is the right way to weathertight a new timber frame shed wall, clad with horizontal boards, joining onto an existing rendered old stone wall?

 

Should I install a lead flashing turned into a slot cut into the render, and turns 90 degrees to run behind the cladding?

 

Or (easier for a DIY'er):

 

Fold a PVC DPC into the corner, concealed behind a vertical batten fixed to the rendered side? As per this post

The shed is a small 2mx1m lean-to to house a house water pump and water treatment kit. Soleplate will sit on single row of concrete blocks, so it is 200mm above ground level.

 

The site is very exposed (Scotland) but the occasional minor leak won't harm anything inside so I'm thinking the 2nd option is the way to go (and I don't have a disc cutter to cut the slot in the rendered wall).

[Hastings]

All done now, no need to respond.