Flying Abroad while Trans

Here's the deal: My son (16) is trans. This next summer, he'll be going to Germany for a school trip. (He'll still be 16). He recently came to me with a bunch of problems he's been stressing about, as he hasn't flown out of the country since he transitioned.

Background info: We are American. He's traveling from America to Germany using Lufthansa. He's going with a group of 7 on the trip. (Including him, 6 students and 2 teachers). Here's the kicker: none of them know that he's trans. He's stealth. (I believe that's the correct term) He passes extremely well and always has. He wears binders (gc2b) and has a packer. He'll be gone for 2 weeks, staying with a female German student and the host family.

He has 3 concerns:

1) That his testosterone will become a "problem". I'm not sure I understand this fear (and I told him as much), but I figured I'd ask. He's worried that his T will cause issues on his way home. He's traveled with his medication in his travel pack before, just never out of country. I told him it would work the exact same as it would if he wasn't leaving the country, but I'm not exactly well educated in how things work in Germany. It'll be on his carry-on in a medication travel bag. It'll have all the needles, syringes, medication, disposal containers, etc. that he'd need for the trip. In the bag he always carries the prescription label.

2)Being trans abroad. I understand this fear, and we definitely need advice. He'll be staying with the family for 2 weeks, and because he's a guy, he and the German student will be in 2 different rooms. Despite this, he's been panicking. He's worried about showering, about what he'll do when his binders are in the wash and he doesn't have one to wear, swimming, and some others. I obviously have no experience with these things, and he would greatly appreciate some guidance.

3) His packer. He asked me about taking it through the airport and I thought it wouldn't be a big deal. Curious, I looked to Reddit. Low and behold, I was so very wrong. I read some posts and replies about it, and I am extremely worried for him. He is extremely bottom dysphoric, and has expressed this many times. He will already be in an uncomfortable situation (being in a different country with people he barely knows) and he doesn't think he will be able to spend the two weeks without a packer on top of that. Keep in mind, he will be a minor, and the people he is flying with DO NOT KNOW HE'S TRANS. Under no circumstances, do I want him to be outed by the TSA. He'll be allowed a check bag and a carry on. Option 1, he wears it: Nothing could happen, great. Or, he could get a pat down and that be then end of story. OR he would end up getting his packer scanned for explosives. This would be more than embarrassing for him, and the adults would have to be knowledgeable of what's happening. I heard that this is dependent on the reason he gets flagged. Is there a way to stop this if I get him a different packer? I'd be more than willing to. He currently has the STP Freely by transguysupply, but he says he doesn't really use it to STP anyway. Is there a packer he could get that would solve this groin flagging? Option 2, it goes in his carry-on: Nothing happens, great. He gets stopped and it gets pulled out and revealed to everyone on account of its shape or that it looks like a gun? I have no idea. He'd be a minor, and imagine seeing a teenage boy getting a dick pulled out of his bag. Absolutely not. Option 3?, he puts it in his checked bag: I saw no entries on this, but I think it might be the best option for him. He'd be more than capable of lasting 1 day without it, so not wearing it during the flight is a much better outcome than not having it for the whole trip. Is this plausible?

TLDR: My son (16) is trans and going abroad to Germany for 2 weeks. He has 3 concerns relating specifically to him being trans. 1:his medication flying to and from Germany. 2: living as a stealth trans person with a host family 3: packing while traveling

Any advice or guidance is welcome, I don't care if you think it's helpful or not.