"Flipping" the axle is a common term but that's not how it's done. It refers to moving the springs from one side of the axle to the other (top to bottom or bottom to top)and usually the axle tube has a built in camber. If as you say yours is just straight then the only thing I can see being a problem is that the axle tube will fill with dirt and moisture causing it to rot through very quickly. I would just have a couple of plate/perch welded onto the bottom of the axle and keep the axle upright but hang the springs under.
