Just a quick follow-up to the numbers, a 23" length of 1.5" X 1.5" 16 gauge steel with take a load in excess of 900#, if loaded in the center & supported on the ends (actually it's good with 20 ga. tubing, .035"). The two 1" lengths have 1/2" holes drilled in them, so they're weakened a lot. With 3 members to take the load, it should be fine the way it's built, but if it fails, I'll let everyone know. a 23" length of steel tube is pretty strong.
Here's a calculator to use if you just plug in loads. Works pretty well. I used a L/D of 360 for deflection.
http://www.atc-mechanical.com/calcul...al-properties/