I think the MDF, dinner plates, etc. and various backings are a great idea (especially the plastic dinner plates), but......
those are for a more permanent mount.
I figured the Ubiquiti mount with T-bar clips might help you temporarily mount the cam, see how it works at that location, un-mount it with no damage or holes drilled, re-locate and when satisfied with the location, go with the backing (MDF, dinner plates, etc,) ...that's when you drill the holes in the drop-in ceiling tile.
You'd only need one, as it would be used to decide where all the cams are to be mounted permanently as you move it from location-to-location on a trial basis.
Just a thought....