Verified.
For bionic I ran
mmdebstrap -v --keyring /usr/share/keyrings/ubuntu-archive-keyring.gpg --aptopt='Acquire::http::proxy "http://localhost:8000/";' bionic bionic-proposed http://archive.ubuntu.com/ubuntu 'deb http://archive.ubuntu.com/ubuntu/ bionic-proposed main'
to enable proposed and this succeeded with
Setting up apt (1.6.16) ...
Verified.
For bionic I ran
mmdebstrap -v --keyring /usr/share/ keyrings/ ubuntu- archive- keyring. gpg --aptopt= 'Acquire: :http:: proxy "http:// localhost: 8000/";' bionic bionic-proposed http:// archive. ubuntu. com/ubuntu 'deb http:// archive. ubuntu. com/ubuntu/ bionic-proposed main'
to enable proposed and this succeeded with
Setting up apt (1.6.16) ...