cp ~/.gnupg/pubring.gpg /path/to/backups/
cp ~/.gnupg/secring.gpg /path/to/backups/
cp ~/.gnupg/trustdb.gpg /path/to/backups/
# or, instead of backing up trustdb...
gpg --export-ownertrust > raine-ownertrust-gpg.txt
NOTE The GPG manual suggests exporting the ownertrust instead of backing up the trustdb, although it doesn't explain why.