Making stealth corners

I am siding a small building with fiber cement planks. The lumberyard has stealth corners from Versatex that are un-Godly expensive. Nice, but really expensive. I like the look of stealth corners, so I am going to make my own using the Certainteed 7/16" trim boards. I need to put some blocking on the corners first.
Would you happen to know the thickness of the blocking I should use? Thanks.
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