Anywhere really. The SUPER-Pro measures 120mmx63mmx27mm. The Active-PLUS and Easi-PLUS 107mmx64mmx23mm. These small sizes allow you to either mount the units on the bike such as under the seat, or alternatively in Tank bags or Panniers. You can even carry the units in jacket pockets (with care of course).
There are really no major requirements, except that the units should be carried where bike vibrations are a minimum. For example, if the units are mounted under seats against the body of the bike, then you should try to buffer any vibrations by using strips of velcro or rubber, or some form of padding. This will minimise the possibility of dislodging components, or scratching the units. General common sense is needed.
Please note that the SUPER-Pro is designed to be bike powered only, and would therefore normally be mounted under the seat or on the bike somewhere. For this reason, the SUPER-Pro has the power-lead hardwired to the unit.Where's the best place to store my Autocom system on my Bike?
The Active-PLUS and Super Pro AVi units have also been designed with lead lengths to allow the unit to be mounted at the rear of the bike under the passenger section of the seat if you choose to hardwire the unit to your bike. Both of these units also have the options to be remote mounted in a tank bag or other luggage as a portable or via a quick disconnect power lead.
This give you the flexibility to mount the unit almost anywhere that is convenient for you as long as the location is not directly exposed to the weather (additional leads may be required depending on your choice of mounting location).