Hi! So turns out the "hand-made tarball" is not manually created by you, but simply the upstream release tarball as-is.
Seems to me your scenario is just a basic upstream import which will be fully automatic with `gbp import-orig --uscan` as long as the debian/gbp.conf, debian/watch (and debian/upstream/metadata + upstreamvcs remote) are correctly configured. See explanation in eg https://optimizedbyotto.com/post/debian-source-package-git/ I will try to send you a MR with these fixed later in the week if I have time.
