Thanks for that David, good to know!
I've done a bit more research today and have a good idea of what I need in terms of primer. Per G6Tanuki's suggestion I've had a look into the Rustoleum range of mattes and there's one called "Robin's egg" which isn't far off what I had in mind; the screen swatch looks quite bright, but the pictures I've found of various real applications seem to have the right muted tone I was going for. Alas, it seems difficult if not impossible to find in the UK! Rustoleum also have hammered options for the lid and that one seems more readily available.
The Takachi enclosures are great in that because they are U shaped and slot together, it should be fairly easy to orient and get good even coverage on each piece.
Thanks again for the contributions everyone, there is some great advice here
Cheers