One weakness of the existing design is that the mounting posts can break when being tapped, or the threads can be stripped during assembly.  The best way to protect the plastic mounting posts is to use heat-set thread inserts.  Note, this only works with thermoplastics. There is an expansion-type insert that can be used on other plastics. 

I use McMaster-Carr part 93365A230. Carefully drill out the 4-40 thread holes in the mounting posts with larger and larger drill bits until you reach 9/64". Try to hit this size exactly (that is, buy a 9/64" bit). Make sure the bottom of the heat-set thread just fits into the top of the hole. With a soldering iron (with a very clean tip), poke the tip into the heat-set thread and hold until the plastic gets soft. With a little push from the iron, the thread will advance smoothly into the hole. Lift the soldering iron off when the insert is completely inside the post. Have a small flat screwdriver handy to keep the thread from lifting up while you lift the soldering iron. There are some good demos in the Internet, so you can see how it works.