Thank you for that response. I note that you have several poles on your design, so that it must take quite a few guys to stabilize them all. But that is what I also see often on European tents used for high winds - lots of guys on the poles.
A while back someone posted a link to a video of a Warmlite tent in high winds without guys - frightful.
About the dihedrals - Just ordered a few and measured them with a protractor. That's where the 30 degrees came from. The kite folks don't seem to think in terms of degrees, so it has become necessary to order and measure. Same with the angled fittings. Makes for great cries of either delight or cursing at the kitchen table. Dearly hope the larger ones I ordered are the same angle as the two little ones ordered first. Expect so.
The size difference between tube and ferrule for both the Easton .344s and .340s is .003". You are thinking about a difference of .006" when the .340 tube is inserted into your carbon tube. Please note Roger's comment, above, about the result of having the tube too loose in a connector.
So I suggest you need a snugger connection, no more than .004" at the most, and ideally, .003".
Also, even if a .344" O.D. tube elbow were available, inserting it inside, rather than over your carbon tube as Roger does, will put a lot of pressure on the lip of the carbon tube. Not so good.
But anyway, I tried cold bending an Easton .344" tube with one of those cheap 3-slot benders that you get from the tool outlet sites ("Pittsburgh - made in China). But the fit was snug, and the tube broke almost as soon as it started to bend. Was in the basement at about 50 degrees F. temp, so will bring a tube upstairs and try again tomorrow at room temp. Will post if that makes a difference. As earlier noted, if I heat it, it will lose the temper - no good for an elbow.
You could talk to a machinist, who might know how to bend the Easton .344 to your desired angle and preserve the temper. Otherwise, the problem is that most of the 5/8" ALU stock, as well as the more tempered but bendable Jansport 5/8" tube, is closer to .4" I.D. than the O.D. of .387". If you drop to 1/2" stock, it is too small.
I guess what I would do, if I wanted a strong elbow and therefore didn't want to play with the softer plastic pipe fittings, would be to get the 9mm (.354") dihedrals , and fill the end holes with high quality epoxy, maybe a putty, and drill them out to .346". Then I would cut 3" inserts of Easton tubing and glue them 2" into the ends of your carbon tube. The protruding 1" should then fit into the dihedrals, and the carbon tubes would be less likely to break because the snugly glued inserts would spread the force over the 2". Sorry I don't have a better suggestion. Consider calling polesforyou.com before making a choice.