Maybe a simple support structure like this...
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You could slap something like that together in no time. If your growing trays are 4X4 feet, you could probably build a support structure out of pallet wood. Just build it to your required height and size. Nice thing about that 2-part design is that you can easily relocate it if needed. Well, the growing trays might be too heavy to move unless you emptied them.

What is PT? Not sure what you are talking about.
I like working with wood. The last year and a half I have made lots of rough, but useful, projects out of free pallet wood and salvaged lumber. If/when the wood rots, I'll just build a version 2.0 of the unit and probably make it even better.

I bought a Flux Core Welder a few years ago for small metal repairs around the garage, but my welding skills are mostly less than adequate. My wood projects are stronger than my welds on metal. I would never trust my welds to support anything of weight or importance. Oh well, sometimes it is good to know your deficiencies and limits.