Here is a solution;
First pic, the basic idea
View attachment 3871235
Next, in use
View attachment 3871236
Obviously you would need it quite a bit larger. Put feet on it where they need to be to make good contact with the bottom cab. I use mine so I have a flat surface for a laptop, interface, phone, etc.
I used Plasti-dip in a spray can for a bit of extra grip and vibration deterrent.
Love it, what a great idea. Simple, extra cheap and very useful. As a DIY guy myself, I can only applaud you. There is nothing greater than DIY solutions.