My P3 is is on all the time in both my Chevy Traverse and my Chevy Silverado. I just disconnect it when I get to the CG.
What bothered me more was that the aux power to the trailer was also always on. To fix that, I installed a relay in the aux power line and a switch on the dashboard so I could kill the power to the trailer if necessary. If you find a wire that's switched, you can wire the relay to that and not need the switch on the dash. (I did this in several of my Grand Caravans when I was pulling a popup.)
1988 Coleman Sequoia - popup (1987-2007)
2012 Roo19 - hybid (2012-2015)
2016 Mini Lite 2503S - tt (2015 - ???)
2011 Traverse LT, 3.6L, FWD
2009 Silverado Ext Cab, 5.3L, 4x4, 3.73
2016 Silverado 2500HD Dbl Cab, 6.0L 4x4, 4.10