The Steam Man — Joe R. Lansdale

On the great plains of the old American west, enormous steam-powered robots march across the countryside. Their mission: to defend the populace against invading Martians and armies of killer albino apes! The Steam Man, a giant metal man operated by a team of monster hunters, seems to have the defense of the West well in hand, until a crazed and powerful vampire comes to town with the intention of bringing forth the apocalypse!