Install XPCR

[Marauder2003]

Please see http://myimagecollection.com/ftp/layout.pdf for a diagram

A is the main panel on the outside of the house facing south.  110F plus in the summer.
B is a secondary panel on the inside of a south facing wall.  Still gets warm.  I have an exhaust fan that triggers at 120F.  It does run at times. 
C is a 3rd panel on the inside of the house.

For product life expectation I would prefer to use panel C for the XPCR.  Would it still serve a purpose there?

The diagram says the unit should be connected to CBs.  Any reason it can't be connected to the CB on a seldom used circuit?

[Marauder2003]

Installed in panel C.  Light blinks when event occurs.  All seems fine.