I think I must have posted this elsewhere, but I ended up using VHB tape also. Instead of Z-brackets, I used "Sticky Feet":
https://rvsolarstore.com/index.php?r...product_id=112
They're far more expensive that z-brackets (though not as much as they are now when I bought them), and are probably overkill, but it made installation on the uneven surfaces of the roof a breeze. Further, the panels are easily removed. They're not special -- just some machined aluminum, and they could easily be fabricated elsewhere. It's just a matter of work!
After I stuck the panels down with the tape, I applied some flexible caulk around each bracket to prevent exposure of the tape to the elements, though I'm not sure that's necessary. They've been on about 18 months now, and they're still rock solid. I'm happy.
Picture attached.
Dave