If I might add to the topic..
Here's mine, Just did it today. (Crap phone pics.. Sorry)
Made it for a EVGA Tegra 4 I got to replace my Galaxy Tab 3, The screen blew after Kitkat 4.4 update..**** YOU SAMSUNG!!!!
It mounts directly to the original mount w/3 small countersunk hex screws w/nuts and washers.
Just a piece of 2.5-3 mm aluminum I had kicking around my garage A little bending/cutting/filing and drilling about 3 hours later this is what I had.
I'd imagine the 8" wouldn't be much heavier than the Tegra.
Just looking @ it now, I'm getting ideas as to what I can do to make it a bit better.. (Pics later)
As it sits, it'll hold my SGT3-7" as well (After I get a new lcd)
Just start out w/ a outline of your tablet on paper, add some extra material for bends/tabs, swap it to cardboard if you're not to sure of yourself then when you're happy w/a design fab it outta your preferred material.
G'Luck.. Have fun.
-D-