What are you going to do in the "off-season"? Is there really an off-season for triathletes? The answer is yes, there is an off-season, but "off-season" doesn't mean inactivity. It's always a good idea to take some time off when your racing season is over, but don't completely quit until the spring thaw. After a good recovery period it's a good idea to stay active. Use the off season to continue to build a solid base, become single minded to improve in one discipline, or use the time to do some weight work.
Freeze your bottles the night before a long ride or triathlon. It will thaw before you need it but it will still be cold when you're ready for it. Something cold will be nice 2 hours into a 4 hour ride!