the bottom of the vertical 10 mounting flange would have a problem with your vent radius..
If it were mine, I would continue the vertical piece to the vent for structural reasons.
Also, I wouldn't bother routering anything except the mounting holes... and that's only if you already have a router.
I'm a screws and glue guy. I'd rather have a strong / structurally solid enclosure which the effort was placed in the actual building than having a weak pretty enclosure where more effort was put into making it look nice than strength.