I have mounted my vices to the posts of the building, which might not be convenient for you. However, you did mention a dirt floor, which I also have. I use a steel plate 1/4 to 3/8 thick, around 12” square, with a hole about 1-1/8" dia. (or whatever fits) in the center, for the vice leg tennon, and four stake holes at the corners. This supports the leg, and keeps it from sinking into the ground. With my big vice, which is mounted lower, the plate is buried about 8" below grade. With my smaller vice, it sits level with the grade - this vice is up higher for lighter work. The plate spreads out the downward pressure from the vice onto the dirt – otherwise the vice leg would be driven into the ground. Hope this is clear enough, and helps.