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The first thing that springs to mind is the method of inserting screws. I would forget self tappers and use machine screws. The hole for the screw will be the std tapping size and as deep as possible. I usually start the thread with a tap or a modded screw about 2 turns deep and then use the screw. It will force the plastic around the screw making for a very strong and servicable thread. Most threads that are "cut" into the plasic will not survive tinkering.
I hope this helps.