Measure the inside of your carport from the roof beams to the ground. Measure from the peak of your carport at the main support beam and at the side beams where the side legs meet the roof. Decide the length for each support post you would like to cut.
Mark the lengths of the desired support posts on your steel tubing. Use a hacksaw or post saw to cut the tubing to length, and fit the bottom ends with ground supports and the top ends with bolt mounts, according to manufacturer's specifications.
Remove any tarp that may be connected to the roof. Move your support posts into place, with the ground mount directly seated, and anchored like your other support posts, below the top position where you'll bolt it to the support beams. Mark the center of the mounting hole for each support post you'd like to place.
Move the posts aside. Drill a hole 1/16 inch larger than the bolts you purchased for fastening through each mounting location. Return the support posts to their final positions. Feed bolts through the newly drilled holes and the mounts on the posts, securing each with a corresponding nut.
Return any tarp to the roof of your carport or use it to reinforce a paneled roof.