Sorry not sure if the title is good.... how do you call the plate above the bottom? Anyway this is what I have done... I used some M4 screws (be careful of the screw length, in the PSU is not much space for screws) and some spare plywood a spacers (made sure the PSU top fan holes are still free) and mounted the PSU this way. I removed the Octoprint too, I will place it in a external case/unit. This may the removal on the bottom plate way simpler, I have only have to do unscrew the 4 Rumba screws and unplug the PT100 and amplifiers from it. Then I can unscrew the bottom plate with no strings attached.
The "plate above the bottom" may be called the "lower-support " This is the part that has the cut-out for the "electronics cover" The "electronics cover" has a hole in it for the fan that blows on the Rumba. So what I think you are saying is that you have attached the power supply to the "lower support" not to the base.
