Very good point, Gina. In the boating industry, it's all about prep, and like you I've seen a lot of failures and re-repairs of various jobs (usually paint
and fiberglass) due to poor prep work.
I don't know enough about the Very High Bond tape to advise for or against it, but I can at least say a couple of things about prepping gelcoated fiberglass for painting
(another time when you want things to stick...).
The main thing that people skip over is to remove the mold-release wax. This is "mold" as in the thing your trailer was built in to give it shape, not as in the yucky stuff that grows in damp corners. It seems unbelievable, but yes, the wax remains on a 25-year-old fiberglass boat that's been out in the air and water all that time. So I'm sure it's still there on the trailer, too.
To remove it you use a solvent. We typically use Interlux 202 (they number all their solvents). I think it's a highly purified acetone, but I'm not positive. The trick is to wipe the surface with a 202-soaked rag or towel (we used special type paper towels), and then immediately wipe with a clean towel. It's easy to recontaminate if you don't always use a clean section of towel for both operations. I mean, not that it's brain surgery, but you have to be tidy or you just smear the wax around.
Once you have the wax removed (and it's important not to reverse these steps, or you'll just "grind it in," then you sand or scuff the surface to whatever the final product recommends (for example, a primer might want you to use 180 grit sandpaper). I'm not sure if the tape would want a smooth or roughened surface, but even if it requested smooth, I'd be tempted to sand with something like 600 or 1000 grit to get a really smooth and level surface. But of course I'd read the tape manufacturer's instructions on that.
Again, this isn't to recommend or warn against the tape, but is just a bit of prep info.
If one were to use the tape, I like the idea that came about later in that Casita
thread to mount only an initial bracket, and then mount the panel to that bracket with a more remove-and-replaceable fastener.
I would like to add a panel, as I got hooked on the "free" and silent power when living on boats, but I can't decide whether to "fit and forget" on the roof, or to have a portable panel. I usually strive to park in the shade (which is not really an option when anchoring a boat
I like the idea of the new, super-thin panels that are "stick on" panels - that's pretty neat. I'm not sure if they're ready for prime time though. In the old days (early 2000's), the flexible type panels had the advantage of putting out power even when partially shaded, but of not putting out as much power ever; while the hard panels put out much more power, but essentially quit altogether the minute even a thin line shaded a section of them. I haven't done my current research to see how that's changing, if it is. So far, I've only been "driveway camping" where there is a handy AC outlet nearby.