That looks good to me, I am new to the detachment but I am no stranger to well built things. I notice on my pack, which was constructed by Rick, the pieces are just zip tied in place, making the items move and shift easily. I would think screwing them in place would make for a better product, but then you will need to reinforce from the back side. Good luck.
Check Scootch's back pack build. His really beefs things up, but then again, you want to be careful and not add too much weight. Your shoulders will thank you...