
I love the comment cut a whole in your shed - brilliant (that's 'thinking outside of the box' albeit a shed).
Thanks for all your suggestions.
I've gone outside, yet again, to have another look at my morso. I think I've come up with good solution. I can remove the long rular section (and not cut it up

). I'll replace this with a wooden length and mark where 60 cm is (as this is the longest length I need). As the moulding is large, the top sliding rular can move along to where I need it (as no 'rails' are needed) and I can cut as normal.
Phew, this may save loads now by getting a shorter shed (what a nightmare).
Thanks
Linda