Thanks for the pics, Ray. I've considered using track like that, rather than mounting to the drip rails. Don't really want to drill a bunch of holes in my roof either without being really sure of myself. Which is also why I've researched the VHB question a little bit.
VHB is in its element if used to attach a broad, flat panel, when you can cover a significant amount of area with tape, to support the weight of the panel. Not so much for heavy loads that attach at a few points. When you take a system that was designed to work with screws, which can handle thousands of psi, and substitute tape, which can handle single-digit psi, without changing anything else, you're setting yourself up for failure. In OP's application he is changing something, in that he's covering as much area as he can, but I just doubt that it's enough.
Re Boywonder's question: yes I've used VHB for stuff around the shop -- mounting signs and whatnot, as well as action camera mounts (which I've seen fail just from a motorcycle helmet sitting in the sun -- tape just lets go), and I know how strong it is. I know that 0.26 psi design stress is underrating it significantly - for short term loads. Think dynamic loading like braking and going over bumps. It's the long-term load with temperature taken into consideration that drives 3M's 0.26 psi recommendation.
BTW 0.26 psi is what I worked out when converting from SI units in the paper I linked earlier. I've seen literature for the American market stating "4 square inches of tape per 1 pound of load (0.25 psi)," but I couldn't find the link when I looked yesterday.
Sure, at any given moment, the tape might be stressed to 50 times 0.25 psi, or 12.5 psi, and not fail. That's because the failure mode to be concerned with for "permanent" applications of VHB is creep, which takes time at load, and happens faster at higher temperature. Creep is the same phenomenon that explains why the pressure sensitive adhesive "wets out" the substrate over the course of 24 hours after application. 3M's guidelines state that you should try to achieve 15 psi in the tape during application to get the process going.
You can see this for yourself quite easily if you take a piece of scotch tape and set it on a smooth surface like glass or plastic where you can see the interaction going on between the tape's pressure sensitive adhesive and the glass. Don't press it down hard like you normally would but just set it there and poke a few spots close together with your fingernail. You will see the tape "connecting the dots" by itself between the spots that you started. This is what's going on with VHB in the hours after you first apply it.
From what I've gathered, 3M's biggest market for this product is architectural facade, like steel panels on a skyscraper. 0.25 psi is what 3M recommends so that the weight of the panels is supported indefinitely. If you exceed that stress you start risking failure due to creep. The wetting out process reverses due the the sustained load and the tape peels off at a much lower stress than what it can handle for a transient load.
I'm not trying to scare or discourage OP; just trying to provide info so he can make an informed decision.
[Edit]: Found the link to the data sheet with more detailed info on 3M's website.
https://multimedia.3m.com/mws/media/...-vhb-tapes.pdf
See p. 7, "Use the right amount of tape."
When I said their biggest market was architecture, that was probably wrong. They're selling VHB to many markets like consumer electronics, signs, etc.
A more accurate statement would be, "Their most safety-critical market is architectural facades." When you absolutely can't tolerate a 100 pound piece of sheet metal falling off the 80th floor...
Vanna
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