I use dual monitors, and have been amongst those who have asked for undockable windows, which would make life a lot easier.
The only way I can see of successfully utilising dual monitors with RadarBox, is by stretching the whole thing across them both, then shifting the border of the "radar" window so that it occupies one of the monitors. Just means that there's whole lot of available space on the other which you can't use, other than for Myflights or similar (although this only seems to work if you have Myflights on the right of the radar window, for some reason). You can't shift the toolbars, etc.
DC