It's nice for locking your helmet to it to the eye-bolts or maybe a 15lb bag tops.
I wouldn't go that far....unless you want to find your 15lbs of stuff scattered all over the road. Sorry, but I gotta call it like I see it. The issue isn't so much what you've built but how it is mounted.
Its location behind the rear wheel travel arc will create moments of inertia that will inevitably cause a failure of either the rack itself or the fairing it is sitting on.
Think of the inertia transmitted through it when you hit a bump. Then add orders of magnitude for each pound of load resting on it. Then repeat for each expansion joint you hit on the freeway.
It would not take a great deal of that before parts crack, starting with the least structurally sound part, the plastic tail fairing. Then the frame of your rack if the plastic base doesn't go first.
I've seen this happen with real deal, specifically designed touring racks made from high quality materials. If it happens to them, it will happen to yours.
It's probably best left as a spot to stow a spare helmet and not much more.
Not trying to be a d*ck but I'd rather you hear it from me and not lose your stuff on the freeway. I'd hate to read your rack failed and you lost your load on the freeway....or worse; it caused you to crash when your load got caught up in the rear wheel.
If I didn't say anything and read that, I'd really feel like a d*ck cuz I could have at least warned you it was possible or even likely.....sean