I think it'll probably be OK for the length of that trip, but it's a bad place for a stress riser.

The seat tube near the BB is one of the most highly stressed area on a bicycle, being pushed down and rocked with every pedal stroke. Seat tube failures near the BB are among the most common non-crash breaks of older frames. see below



On the bright side, this kind of failure is among the least likely to cause a crash or injury. Speaking from first hand experience, it can be field repaired (won't be pretty) with readily available stuff and a bit of creativity.

So, as I said, enjoy the tour, and after that ride it as long as it lasts, but if/when you start to hear creaks or clicks as you pedal, you know where to check first.