Isolating the HSTNS-PD18 negative/ground from earth/chassis

I've bought 4 HP HSTNS-PD18 (aka DPS-750RB) server power supplies to build one big 48V 3kWh powersupply. The PD18 is 12V by default.

By default the negative/ground from both the AC and DC side are connected to the chassis/earth. If you want to place these supplies in series the DC side needs to be floating, otherwise this will cause a short.

Here is the power supply disassembled: 

Luckily for me the DC side is only on 2 points connected to the chassis, with these two screws:

Who connect to the buttom of the PCB here:

And on top via the screw:

What I did is filed the tapholes down about 2mm, like this:

Which allows me to place a nylon m3 nut in there:

And together with a nylon screw from the top:

Isolates the negative from the chassis, and secures the PCB like OEM.

I will show you the final result in a next post.