Eternabond tape. I use it on all seams. Never had a leak . Be careful when applying , once it’s on its on for good .
I have a small water spot inside the trailer that seems to align with water being sprayed during cleaning into the seam just above the decal. Can I just run a bead of silicone caulk along there? Don’t worry about it and be more careful when cleaning?
You can put silicone or another suitable sealant there if you want, I’ve seen some trailers come with the front tin siliconed at the seams on the front from the factory.
That being said, if the tin is put together properly water shouldn’t really be able to get in there unless you’re like sitting there with a pressure washer pointing it directly into the seam.
Are you sure it’s not getting in through the lights or the roof seam? That seems more likely to me.
I would check the sealing of the market lights.
The other thing I can think of is that, at the seam, the sealing has failed on the top of the seam, but is still good at the bottom. This will cause water the fill the seam behind the trim and can overcome the natural water tightness of overlapped panel joints
