(First, do you want a new topic for each thing we find, suggestions, etc? If so, then lock this thread – otherwise I’ll keep throwing stuff in here.)
The square that shows the dimensions of the device needs to float on top of everything. Once you stick a large background image in the scene you no longer have the ability to place things according to the edges of the device.
And if you could XOR it or something that might be handy in case the background is black or another dark color – so it will be visible no matter what.
Jay