Pressure changes with temperature

My kegs are in the kegerator at 38 degF.  My CO2 tank and gauge setup is outside the kegerator.  The whole setup is in the garage.  In the morning when the garage is cool the line pressure is much lower than the line pressure in the middle of the day when it is 90 degrees in my garage.  The change in pressure throughout the day is at least 5 psi.  Where should I set the gauage?  I like the bottle outside because I can see the gauges but I'm at loss on what to do with the pressure setting.

Is it the Line Pressure or the Bottle Pressure? I would think that the Line pressure should not swing that much because of the regulator on it, but the bottle will because of the liquid in the bottle. I keep mine in the fridge with the kegs so it always reads low. I use 10-12psi for everything, as long as it has bubbles, I'm happy.

Cheers
Preston

I have only kegged one batch of beer, so I am not an expert here.  But I think the following is how CO2 pressure works.

The goal is to get a certain volume of CO2 into our beer.  Say for example 2.01 volumes.  That can be achieved at different temperatures, using different PSI.  

We could achieve a volume of 2.01 CO2 by force carbonating in a keg at 35F using 5 PSI.
We could achieve a volume of 2.01 CO2 by force carbonating in a keg at 40F using 7 PSI.
We could achieve a volume of 2.01 CO2 by force carbonating in a keg at 45F using 9 PSI.

See the following chart:  http://www.kegerators.com/carbonation-table.php

So if your beer has a CO2 volume of 2.01, then it's PSI will be lower at lower temperatures, and higher at higher temperatures.  But the volume of CO2 should be the same.

Use a carbonation chart, or the BeerSmith carbonation tool to help set the desired volume of CO2.

This is my understanding on CO2.  If I have any of this incorrect, then please let me know.  I hope this helps.