Before you touch flame to those tubes, get a bunch of tube ends (Aircraft Spruce sells boxes of grab-bag tube ends) to practice with. Practice your miters. Practice fillets on multiple angles. Find out how difficult it can be to control the heat and flow of the bronze. Get comfortable with flicking the flame onto and off of the joint. Use a lot of flux. Then, when you're comfortable with all that, run a set of 10 more fillets before you start in on the frame tubes.