Help with design...

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I have been tasked to build a grape vine support for my father.  I want this thing to last a long time, so I am probably over-engineering it.  A rough design sketch is attached.  I plan on using 3/8" eye bolts through the 2" square pipe.  I am going to weld the washers and nuts onto the pipe, but not the eyebolts so they can be changed out if needed.  The turnbuckles are going to be used to tension the cable between the posts.  I am going to use aircraft cable for the cables.My main question is, do I need to put a sleeve inside the square tubing between the two holes to provide rigidity?  Looking at the image, that is what the dark blue rectangle is representing.Thanks for the input! Attached Images
Reply:Looks like 11 gauge is around 0.11", so that's fairly beefy.  I assume this thing will be pulled very tight and you are concerned about the tube defoming.  The sleeve seems like a good idea, but it may be easier to just use a large diameter thick washer on the back side to distribute the load.
Reply:Yes, my main concern is the tube deforming from the tension on the cables.  I don't want to dimple the square tubing because of the washer and nut trying to pull through.
Reply:I think the sleeve is a good Idea, but I personally don't think you will deform 11ga tubing if you just use a larger machine washer.I'm a Lover, Fighter, Wild horse Rider, and a pretty good welding man......
Reply:I would only weld one of the nuts to the pipe. It will be much easier to change out the eye bolt that way.
Reply:It will be fine the way it is beyond your lifetime..Your not holding up a bridge.. My Grandfather had tons of vines on "hemp" rope suspended from 2"dia steel poles in the ground..And it lasted forever..Untill... No we did'nt smoke it.. But your set up will last a very long time..Unless a tornado comes by... ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:If that bolt is threaded all the way through, use a total of three nuts & washers....one where you show it already, another just opposite it on the inside of the tubing, and another also inside the tubing on the other end of the bolt. That will prevent the tubing from crushing.
Reply:Your biggest problem will be the tube rusting out in the ground.  A big washer on the far side is all you need.  If it is going directly in the ground some zinc based paint is in order.  If in concrete make sure the concrete surface is above grade and sloped away from the tube to prevent water puddling.  Maybe cap the top???
Reply:OK, thanks for all the suggestions!  This forum is great!The steel supply place only had 16 gauge when I got there.  I ended up putting nuts on both sides with washers under them and the sleeves.  My dad is a retired engineer and I usually end up over-engineering everything to satisfy him....  The posts were set in concrete and we did slope it away to prevent puddling.  I capped the posts as well to prevent them from filling up with water.  Unless the ground water rises, they should stay pretty dry on the inside.BTW Zap, we do live in a tornado alley.  Its been about 10 years since the last "big" one, so we are due for one.
Reply:You could also use a flat stock that matches the size of the tubing, drill it and make your own washers, choose the thickness you like for the flat stock , 1/8, 3/16 is plenty and will transper the load to the side planes of the tubing , won't distort this way."Si Vis Pacem Para Bellum"Lincoln Idealarc 250 AC/DCMillermatic 251   Syncrowave 300   30A spoolgunLincoln MP210Hypertherm 45(2) LN 25(2) Lincoln Weldanpower 225 CV(4) SA200   1 short hood    SA250    SAM 400
Reply:BTW Zap, we do live in a tornado alley. Its been about 10 years since the last "big" one, so we are due for one.