Agreed! Brass is totally fine from a temperature perspective in this situation. The issues I would be concerned with (but not that concerned) would be galvanic corrosion and any potential incompatibility with substances in the coolant. Brass should be fine with all the substances in the coolant, as it's mostly ethylene glycol and I'm 100% sure they use brass for cooling systems in countless other situations. The galvanic corrosion is probably a non-issue. as there's plenty of aluminum in the system, and I don't even know that coolant is conductive, so it may entirely be a non-issue.The brass Ts are marketed to home plumbing systems which are not expected to reach over 160F. They are not marketed towards automotive uses, hence @thetut’s question. The manufacturers guarantee 160F because that’s what their market demands but they have not been tested to see what their true upper limit is.
As for doing it before your trip, I wouldn't worry about it. Take a trusty roll of duct tape and some wire. If it blows, tape it together with duct tape, wrap it with wire and then tape it again and continue your journey. But it almost certainly WON'T break on that trip.