Hordes of the Things is a generic rules set. Armies are broken down into elements
with clearly defined roles (the army element of "Sneakers", for instance, represents
trackers and infiltrators. Sneakers can move through other base stands, friendly
or enemy).
They've made their rulebook available as a free pdf
http://www.wrg.me.uk/HISTORY/HOTT2.pdf
Witterquick: Are you using the suggested base sizes? How well do the 28mm
models fit using that scale?