If anything, the nicotine will break down before the flavor of the juice will. Refrigeration might induce condensation, and that's not necessarily a good thing, either. Stick the juice bottles in a cabinet low to the ground, carry em with you, but keep them out of sunlight. Heat and light can degrade nicotine, there's a chart somewhere that I lost in all my random and careless browsing, but I believe it was based on leaving the bottles in or near a windowsill.
Definitely don't stick them in the freezer unless you can put them under vacuum. There's an even higher chance of condensation when air is inside of a container under such low temperatures.
I would personally be more concerned about the plasticizers in cheaper bottles going into the juice under high temperatures than nicotine degradation, but I'm concerned about everything; that's just me.
The only thing I ever seem to take with me on the go is an ammo belt of cartomizers, multiple CE2's/CE3's, or sometimes a DCT. I used to carry the bottles, before I took a break from dripping.