I use pine needles (in Maryland) and they work well.
The perlite and screen just seems like overkill. Like when people use landscape fabric but find out things don't work as desired, then the fabric is a nightmare, a lot of work to remove. Perlite is also bright white. I think it'll leak out from the frame.
Maybe I am not being open minded.
also I am not sure 2 inches of perlite will really block seed germination. Put 2 inches in a large clear plastic container and shine a flashlight underneath, can you see the light?
And creeping weeds with rhizomes, like some grass. will go right under and come up. Then you're in the 'landscape fabric problems' boat.
I used straw in the vegetable garden with good results this summer, was much better at weed blocking than I expected.
I go for natural mulch which becomes a soil amendment over time, such as pine needles or straw. Blueberries have fine shallow roots that would really like the pine needles or another organic surface mulch.
Remember your local university extension service for good advice
https://www.montana.edu/smallf...
