Idea's are great - I can see pros and cons which to a great extent depend on the execution!
1.
Water collection - the IBC's will be heavy when full,
but if you then use the collected water, they're now lighter again and may no longer give the stability you need? Water is pretty heavy stuff, and I'm no Engineer, so I expect calculations could be made for your wind conditions that could tell you the minimum water level in each IBC to still provide the stability you need.
2. Portability - How were you thinking of moving this structure? Will it be easy to dismantle into manageable sections? Personally, the image you posted does not seem rigid
enough to use skids to move it, but that's something that could be built into the final design. How "portable" do you actually need it to be? My friend has a "skidable structure" because that way he doesn't need to get a permit. I doubt it will ever move! However, assuming your image is a group of
solar panels. I could certainly imagine situations where solar panel location could change with the seasons to get the best solar gain balanced with the lowest wind risk.
3. Foundation - just because something's "portable" doesn't mean you can just skip the foundation part! Many people underestimate just how much the level of the ground changes over a 15' by 15' square. I've built enough raised beds that I *think* I've finally learned that lesson. Either the superstructure would need to be adjustable based on the level of each tote, or the ground has to be adjusted so each tote is level with each other tote.
4. With the
footprint of an IBC, there could be settling under its lower frame as the weight isn't distributed evenly the way a flat surface would be. There are areas and times of the year where I would worry about uneven settling on my
land, but so much "depends" - soil type, moisture level, etc. In my climate, I'd have to pay attention to where the run-off from the superstructure would go. It could be as simple as digging a bit of a trench to direct the flow.
5. UV degradation of the IBC's - this can take years, but it would be something to be aware of and plan for.
Those are the things I'd consider during the design phase off the top of my head. If you could build modularly, such as a single tote holding only the number of solar panels it can hold, so of the issues would be reduced, but it also would easier for "tippiness" to become a significant limiting factor, at least where I live.
Someone else here did you a giant version of a rock jack to support solar panels on one of BC's Islands. That might be another option depending on you ecosystem - remove the rocks to move, pile the rocks back on for security!