This isn’t my territory, so excuse my ignorance, but I’d love to know how
There could be issues with the TPM chips, having to re-enroll fingerprints or something, but not a problem in the case of a border search, since they can't pull out anything. So you could backup your whole system, install a clean ubuntu without anything special on the system (just if they check), and then download the image wherever you are and do whatever you want.
So on a Luks encrypted xubuntu, o can dd to an external and then my laptop can fall in a lake the next day and I run some simple command to unwind that on a fresh laptop and I’m off to the races?
I presume it’s much slower than rsync, since it’s comprehensive each time.
Are there any gotchas?
This sounds too simple to be true—but again, my knowledge on backup is very unprofessional
The problem with dd is, that you can't really run it on a running system, because stuff is constantly being written to the drive (this is same for rsync too, but usualy the damage is smaller), so you have to boot a live linux from usb, dd the whole drive to an external drive, and then after swimming ashore, boot a live linux on the new laptop, and dd the backup to the new drive.