I used a vintage Delta 12" disc sander to get the angles required for each tube.  I have it rigged here to assist with getting the ends of certain tubes square and cut to final size. The assorted angles cuts were done without a jig. 

My original thought when I purchased the band saw instead of a chop saw was that it would be quieter and I wouldn't have sparks flying around the garage. I live in a residential area I was concerned about the noise from a chop saw bothering the neighbors.  In hindsight, I should have said 'screw the neighbors and bought a chop saw.  Most of the tubing requires angles cuts (80 degrees, 50 degrees, 140 degrees, etc).  It would have been easier to mark the tubing at the desired angle, rough cut it with a chop saw, then use the disc sander to finalize the angle.  Instead I use the disk sander to sand down to the final angle.  No problem on 80 degree angles.  It's a pain in the ass for those 140 degree angles !   The chop saw would also take up much less room in the shop.

Protractor Tools 'n' angle stuff

I tried this type:

Cost: about $6 at Princess Auto.  I didn't find it very useful for the tubing.  While it is easy to use, the tool is very thin.  The square tubing is chamfered.  This tool would not sit squarely on the tube and allow an angle to be marked with any consistency.

So I tried this tool:

Cost: about $2 at P.A.,  This tool is thicker and will sit nicely on the tubing the ensure consistant angle marking.  Useful tool !

I also tried this one:

Digital Angle Finder from P.A.  Cost: ~ $40 or so.  This was an indulgent purchase 'cause I'm a tool whore !  <grin>

You want a 72.6 degree angle ?  This thing will do it.  While it is a little cumbersome to use, it has it's place.

Update:  I found setting the the digital protractor to the desired angle and then transferring the angle to a sliding t-bevel worked very well.  My thanks to Rolf for the advice!

Here's the rig:  Lincoln 155 with 72/25 argon mix bottle with .030 gauge wire:

I tried some cheesy corner clamps from Canuck Tire, but I found these magnets from P.A. worked very well.  About $3 each if you get them on sale.