Thank you all for your help!
Adding...
It looks like you may not understand the principle design?
The uprights should span across the joints of the horizontal boxes, not directly inline.
On a small stand like this you only need four uprights of exact length. You certainly can make an L-shape upright by screwing two together. But in my experience the inner pieces that hold it all together for assembly are well worth the effort. So I use three(3) 2x4s in each corner, not two.
Sorry, I'm colorblind so I suck at pointing out the components by color!!!
I believe the uprights are purple??? Those eight(8) pieces need to be exactly the same length and sit firmly between the two horizontal "boxes".
@DaddyFish Don’t worry, I’m colorblind too, so I get what you mean by purple haha. What do you mean the uprights should span the joint of the horizontal box? Comparing my attempt to the picture you posted, I’m having trouble understanding the difference. Can you explain a little more?
Many people get into trouble building stands by assuming the concrete floor they are using is actually level.
Shim your bottom frame box until it's level. Make sure your shim material protrudes well into the corner so it keeps the inner vertical tie-in pieces spaced up as well. You don't want them to protrude below the bottom edge of the lower frame box.
Then set the four corner "units" in place, sitting firmly on the bottom frame box. Run one screw from each inner vertical piece (the one that's for assembly purposes) into the bottom frame box.
Next add your top frame box and press it down firmly at each corner as you add one screw from the inner vertical.
Now check your level across the top. Assuming your verticals were cut to exactly the same length, It should be just as "true" as the bottom frame was.
Finally you can add your top plate and the rest of the screws. Don't overdo the screw count. The screws only hold everything in place for transport and basic lateral stability. The weight of the tank and water is supported by the union of the top/bottom frame boxes and eight vertical spacer posts.
To make sure I understand correctly, you're saying to take the following steps:
1. Build the bottom frame box (how can I make sure this is level if the wood is curved? One issue I had was, even though I had a flat work bench, the frame boxes were still wobbly after everything was put together, either on one side, the other side, or both.)
2. Shim the bottom of the bottom frame box to make sure it's level.
3. Attach the corner pieces (assuming these pieces should already be assembled, as in I should have four sets of three 2x4 vertical supports, each with an inner vertical and two verticals that are the actual supports?).
4. Add the top box frame. If the 2x4's are good enough, this should be level as is.
6. Add the rest of the screws. Is 3 per joint between the frame boxes and the inner verticals good enough, or too much?
5. Add the top plate and other finishing touches.
Should I be using glue for the joints? And what about clamps? I think the clamps are what got me into trouble because it pushed one corner of the upper frame box too tight onto the vertical leg, causing it to bend and making the top unlevel. Would it be okay not to use those and just push the top down with my hands instead?
Also, I've been using glue with deck screws. Should I be using regular construction screws instead, 2-1/2"?
Thanks again for your help! I know I have a lot of questions. I've been working on this attempt for a couple weeks and I'm trying to get as much information as possible to increase the chances I'll be successful with my next attempt.
