Hello,
@another sean.
I understand where you are coming from and your concerns, given that I have lived with reactive tinnitus for many years.
However, I've traveled many times with all types of transportation with reactive tinnitus, and it turns out that the fear of worsening is bigger/more of a stress factor than the actual risk of getting any permanent setback.
I'm not you, but I think you are overthinking scenarios here. If you are using sufficient protection for your ears, say on a plane, you will probably have ear fatigue and a spike. Hours, days. It's hard to tell, but usually, it won't last for a long time (weeks +).
If you calm down before a trip like this, your ears will also be less tense, which will help a lot in these situations.
Unless your LDL levels are very low, you will be fine. You will probably be stressed about it, tense up, have some fatigue, and maybe a spike, but in the end, it will be okay. That is the most likely scenario.
Personally, it's an easy choice. Plane. 30 hours on the train will probably give you a lot more fatigue.
Good luck with whatever you choose!