This historical document on worm farming has instructions for
a big outdoor box set in the ground in Section 3, Lesson 4,
"Housing the Earthworm Stock." Assume that scientists know more
about earthworms now than they did then, and that your most
economical feedstocks for the worms are not necessarily what
they were then. Still, what he recommended worked, which is
why he wrote it up as what was probably a lecture series.
http://journeytoforever.org/farm_lib...oliverToC.html