New 18 foot gate frame

I've been welding on the gate for the rental property.  I've used 1 inch, 11 gauge square tubing.  The gate frame is 18 feet long, by 6 feet tall.  I'll mount a wheel to it on one end, and weld up hinges in an uphill configuration on the other end.  Pictures are below.  I ground out the welds on the sides to help the boards sit flat when the pickets are mounted.  I remembered after the first couple that the pickets won't actually touch the frame; only the 2x3 cross boards will.  But I ground out the rest of the welds just to be consistent.  Anyway, I stood it up and put a 4x4 under each end, then had my wife stand in the middle.  It didn't bow much, definitely not enough to touch the ground, so we'll see how it does with all of the wooden pickets attached to it.

We bought the metal at the Fort Worth www.discountsteel.com retail store.  I had them cut the 12 foot pieces in half so that I wouldn't have 10 feet of tubing sticking out of the back.  Then I cut one piece in half to give me two 6 foot pieces to weld to 2 of the remaining 12 foot pieces.  I don't have any way to mount them straight, so I laid them on the floor of my garage clamped to a 4 foot level on the side, then welded across the top.  Before I flipped it to the next side, I ground that weld flat so it wouldn't interfere with the level.  It worked out pretty well on the first piece.  But I took too long on one side of the second one, and it bowed up.  I might have been able to use another level and clamp across the bottom as well, but I don't know that I could have supported it well enough to keep it from bowing.  Oh, well.  It doesn't look too bad, and I don't need to be that picky.