There seems to be a problem with your archive key:
E: Release signed by unknown key (key id F7E974E9405422DD)
elgar:~# keyid=F7E974E9405422DD ; gpg --keyserver subkeys.pgp.net
--recv-key $keyid ; gpg --armor --expo
$keyid | apt-key add -
gpg: requesting key 405422DD from hkp server subkeys.pgp.net
gpg: key 405422DD: public key "Thorsten Glaser (Package signing key
for wtf debs) <tg@freewrt.org>" impo
ed
gpg: no ultimately trusted keys found
gpg: Total number processed: 1
gpg: imported: 1 (RSA: 1)
OK
elgar:~# debootstrap --variant=buildd
--include=apt,wtf-debian-keyring,debian-ports-archive-keyring sid
rg/chroots/buildd/unstable/ http://www.freewrt.org/~tg/dp
I: Retrieving InRelease
I: Checking Release signature
E: Release signed by unknown key (key id F7E974E9405422DD)