Thank you guys, this is all really useful and great to know.
@mikep - your solution there is very elegant.
@patofoto - I didn’t actually setup and stock infusion 360, I just setup the part I wanted to make - should I add this?
The clamp/wedge solutions look great, but not sure how I would implement on this design - It’s not just cut outs/holes but I’m trimming a few MM off each side and rounding corners. On my previous mill I use double sided car foam adhesive - it has very good holding properties and can be removed quite easily - However this won’t be suitable for all projects. I will need to drill my waste board or create something like you have above in some thicker MDF… I also want to make a clamp mount so I can use this on projects I am tempted to make a thicker waste board anyway - stock seems a bit thin?