Thanks for asking (above). I strongly recommend AGAINST using Coroplast as an intermediate layer. It would create two bonding surfaces, each of which must drain away any water (or water vapor) which gets underneath, and VHB tape by itself provides all the stretch-handling which you need. Although my current installs are all with semi-fexible "shingled" panels, I have also had great results with using VHB tape on the underside of Z-bars. (Avoiding screw piercings in the RV roofs.) I have always used an extra z-bar or two, along each long side of "solid" aluminum-framed panels which I have mounted in the past.
The BIG advantage with VHB tape is the flexing foam layer in the middle. The steel, aluminum, or rubber roof substrate will not expand and contract at the same rate as the panels above, even when they are at the same temperatures (and the panels generally get much hotter than the RV/Trailer roof.) The two adhesive surfaces must remain remain firmly attached, while the foam layer handles the push-and-pull of panel above and mouting surface below.
Either go with 'solid panels' on Z-bars, providing air underneath, or let the roof take the heat from the panels. With aluminum or steel RV roofs, panel heat goes through the and gets spread pretty quickly from underneath, radiating back off from uncovered sections of the RV roof. With fiberglass or carbon fiber, the panels get hotter - but the tape handles it just fine. In all of my installs, no one has EVER reported failure or peeling of VHB tape back to me.
In two instances of removing failed panels from painted aluminum and painted steel respectively (after 2 and 5 years), I've had a very challenging time weakening and peeling VHB away the substrate bond. Depending on the fexibility of the RV roof, structure, I prefer the thickness which used to be called "RP-25" on the stiffest of Roofs (Class-B Conversion van steel), and "RP-32" on super-flexible Carbon Fiber or intermediate-flexing fiberglass and aluminum. But again - the most important concept is to attach only around the perimeter, with just a couple of smaller 5"x 1" segments across the middle of the panel (well separated from each other). Around the panel, I always use 5-6" strips separated by 1" gaps. Water can get forced in, but it is also free to exit underneath - and to simply dry off as water vapor, when panels again bocome warm under sunlight.
I have used VHB tape with Z-bars in mounting a few "solid panels" as well, although I have always added some extra Z-bars along the long sides of those panels. As with the flex panels, the roof-to-z-bar bottom tape has NEVER loosened or given way. But I have taken care, in those two installations, to strip the pain completely of from the metal substrate, sanding for extra adhesion strength (P400 wet, equivalent to about 300 grit in ANSI and painting exposed metal afterwards. When finally removing those two panels and replacing them semi-fexible "shingled" panels, the VHB underneath each Z-bar took almost 15 minutes to fully remove.
These installations have all travelled at greater-than 70 MPH speeds for many hours at a time, plus prevailing winds. No panel mount has ever given the slightest hint of sliding or peeling loose.