If I could press and hold the middle mouse button to pan the mockup around, that would be great! (or alternatively make it configurable).
Yup, it’s a great idea, @FredL.
A couple of other folks have asked for it as well. I will give it a bump.
If anyone else would find this useful, reply below, or like this post.
I also think that would be helpful since I know these way to pan from other software.