The 26-year-old has been without a club since leaving the Withdean after failing to agree a new deal with The Seagulls and recently had trials with Kilmarnock in the SPL.
"Bas will give us a more physical presence in both boxes and take some weight off Gary Alexander's shoulders," siad Lions boss Kenny Jackett.
"We've got some good players but we've lacked a bit of strength coming off the bench since Adebayo Akinfenwa left."