I installed mine down. No problems. Used the spacer as well. Ran the air lines through the frame to the back bumper. Took two of the bumper bolts out on the bottom and evenly spaced them and put the valves there. Easy access, easy to fill, and convenient. Works well and looks good too.
A tip to install the bags: take the black cap off, roll the bag as tight as you can, replace black cap, and install into the spring. Works every time.