There are too many reasons to run a lathe in reverse to try to explain, but it is critical to many operations.
For example, I recently needed to cut an 8 degree angle on a part that was too large to feed from the front, so I reversed the lathe and cut the angle in reverse using the compound.
A used South Bend is less likely to break and is more serviceable that anything made in China, in my opinion.
If you can build lego's, you can work on a South Bend.
Yes, the lathe would do what you are asking, you would be limited by the size of work that would fit in your chuck and the length of the bed and small cuts would be required.
I suggest you consider a South Bend, you could probably get a good quality machine for just a little more that you are...
I use a piece of 2X4 and two clamps. Clamp the tube to the 2X4 and cut.
Or, sometimes I use a drill press vise. Clamp the tube in the vise and make your cut.
Basically, look for ways to make your round stock square.
http://www.weldingtipsandtricks.com/index.html
This is the most comprehensive "learn to weld" site on the internet, imo.
You are getting very good advice.
Thank you everyone for the most helpful replies.
Now that I know about the awning rail, I will run that along the top as suggested.
For attaching the bottom portion I am planning to weld in a rail like the one pictured below. This shot is of a new awning I saw going up last week.