Upgrade without Internet access

[Lee Nelson]

I feel like this should be an easy question to find an answer to, but
an evening of frustration and search has found me nothing.

I am trying to upgrade two systems from 12.2 to 13.0.  However, over
my very poor-quality satellite Internet connection,
sudo freebsd-update -r 13.0-RELEASE upgrade
always fails:
....13160....13170....13180....13190....13200....13210....13220....13230....13240....13250....13260....13270....13280....
gunzip: (stdin): unexpected end of file
2354a6afb867bb4e6206b58be4804d4307b9048c8767ac52081be80c162cf8d1 has
incorrect hash.

I don't know whether some sort of timeout kicks in or my provider is
causing enough interruptions that the connection dies, or..... who
knows?  This is life with satellite Internet.

Is there some way to upgrade an existing system without (or with
minimal use of) an Internet connection?  Is there some way to
pre-fetch the files onto portable storage while using a stable
Internet connection elsewhere?  Is there a way to upgrade from an
ISO/USB? I have a 13.0 USB img file, but booting ftom it only seems to
have the options to install or use the live cd, not upgrade.

I have many OpenBSD machines. For them, I download the install files
once and use a local http server to make them available during
upgrades.  Is there some way to do something similar with FreeBSD?
-- 
https://keybase.io/nelsonov