We have used square fiberglass for the last two years. It comes in 1" 1.25" and other sizes. We get it from Max Gain, a supplier for the Ham Radio industry
http://www.mgs4u.com/fiberglass-tube-rod.htm. The wall thickness is .125" The 1" is about the same mass per foot as 3/4" thin wall Al. Fibergalss cuts very easily with a hack saw and drills best with pilot point bits. We use a vacuum cleaner to get the dust while cutting or drilling. It's very tough, we do put either spacers or 3/4" square ldp to back it where we bolt through, just being excessive.