I found these neat military surplus fiberglass stacking mast sections at Mountain View Surplus. Each one is 4 feet in length, and has a sleeve section of about 5 inches in length that inserts into the next section. Paul, the fellow at the store, tells me they were intended to hold up camouflage.
They're great for holding up all the temporary antennas I've been building. One great thing about them is that the inner diameter of the taper section of some (but not all) the masts I bought exactly matches the outer diameter of the PVC pipe that I used for the antenna bases of my verticals. I have 5 of these mast sections, so it was really simple to elevate the 20 meter vertical I built to 20 feet.