In truth, I don't really know all that many big mech things. Battlemech's just a little too... not good design-wise for my tastes, and I've actually not been into all that many giant robot anime or mangas. So a Mack strapped into a giant robot? What would it be?
A shipping container with one end opened up, a hole cut in the top for their head, and arm holes so they can stomp toward the clearly-more-advanced villain of the week in their deadly, competent mech like Ned Kelly.