Wow...first, I'm envious! It sounds like a great trip.

I just started base building for the "off-season" <~~~not that we truly have one here in California. That means long, steady distance at a lower intensity than I would normally ride at. Most of my events are ultradistance (double centuries) so this should help with my endurance. Closer to the start of the season, I will begin to do some speedwork. You can accomplish all of this on the trainer (not promising it will be fun) but it can be done.