Here's my triumphant (by triumphant I mean still in a bit of sticker-shock...) return from Alan Steel. That's somewhere around 400lbs of steel, and I was happy that I got it all to fit in one trip. I saved a few $ by not having the yard do all of my cuts; I had them cut the tube into 6' lengths; any longer and I wouldn't get them into my car. I kept the cutoffs, which you can see on top. I did have them cut all of the slats to length. I have a small metal bandsaw which is perfect for cutting down the tube, but the slats would be too much for it. Plus, at the yard, they can cut through this stuff with ease.
Here's my basic setup for drilling the blind holes in the slats. Each slat is about 35lbs; doesn't sound like much, but it really adds up when you're manhandling these things around!
I knew that alignment of the threaded holes in the slats with the through-holes in my tube trusses would be an issue. If I wasn't careful, I'd have big tolerance stack-up issues. I came up with a workable jig setup to get the hole spacing consistent, and which I could use as a reference later when I drilled the trusses.
This is slow going work, for sure. I tried to progress carefully, with plenty of cutting fluid and patience.
I broke my original bottom-tap pretty early on, then went to a proper machine shop supply store (Dan-Mar, in San Carlos) and picked up a flat-bottom "Turbo Cut" tap, which worked like a champ.
Side note: Go to Dan-Mar if your ever in the area and need machine shop stuff. It's another one of those old-school shops of the kind that seems to be disappearing too quickly around here. They are super friendly and knowledgable, and they really took the time to try to understand what I was trying to accomplish, and what I needed for the job.
-Jake