On 09/08/2019 22:27, Tricky Dicky wrote:
An easier but less neat approach is to use UPVC trim which is quite inexpensive if you can source it from a UPVC supplier rather than the sheds. Mitre the corners attach with double sided tape and finish off and seal with silicone.

Poster already suggested this and I have a few off cuts so will try that
tomorrow and see how it goes, that still leaves other options open.