Are you riding solo, or is this a tour? I would add some interval training rides or do them on the trainer, depending on where you live and weather. Do some out of saddle drills (work up to 5 min each X3 with some rest in between, then add length and # of reps to simulate hills). Other than getting more long rides in, sounds like you'll be set. Increasing the mileage is the easy part, just ride more. Intervals are the way to go to get fast(er).