Greg.., I spend most of yesterday reading the over forty pages at the Escape forum thread that I referred to in my second post and other threads there as well on the subject.  

You synopsis is spot on, well said!  Even with AM Solar's claim (and 3M's marketing), I do agree now, that VHB alone is not to be trusted with such a high liability install (flying panels could cost you a million dollars in a lawsuit). At least for traditional glass panels.

But if putting holes in the roof, why use tape at all.  Four through bolts with backing plates should be sufficient, no?

But will the 1/8 inch thick  fiberglass itself be too stressed, not that the panel would come flying off but the fiberglass might crack from the high wind forces on the panel?    Yesterdays's post about the cracked fiberglass by the door on a 2014 unit has me worried.

What about  sanding off the gel coat and using some 5200 to attach some sort of mounting blocks of some sort?  You might never get the blocks off but the brackets could be made removable and the blocks on the roof would not be that bad (should one decide to do away with the solar panel).

Well Eddie, you and I are in about the same stages in the project so let me expound on my thoughts and research.  I will be discussing a 2015 Scamp 16 with roof air conditioning and the following is mostly opinion and just thinking out loud, so don’t assume I know what is best.

PV Panel selection:

The curved roof and raised center section makes it harder to mount a rigid panel and while it is tempting to consider some sort of flexible panel that might be mounted flat on the roof, IMHO we should rule out flexible panels until the technology is improved.  Most people will want at least a 100 watt monocrystallin​e or polycrystallin​e glass panel, and that means a physical size in the general area of 47 x 21 or 42 x 27 inches and about 20 pounds.

Panel placement:

It might be possible to fit a PV panel on the 35-36 inch-wide raised center section of the roof with the shorter edge parallel with the trailers front (leading) edge and this would result in a little less air resistance while driving than if the panel were turned 90 degrees.  However this would require that the panel be near (or up against) the AC unit and/or extend too far over the front of the trailer. In the first case, the AC unit would sometimes shade part of the panel making it less efficient.  In the latter case, it would create an air dam and the uplift on the panel from the airflow while driving would be substantially increased. It seems that, for a typical 100 watt PV panel on the roof of a Scamp 16 with AC, the dimensions dictate that it would perform better if it were mounted lengthwise across the front.  The ends would then be over the non-raised sections, in front of the bath vent and fridge vent on my trailer.

Panel Mounting:

The primary concern with placement and mounting has to be the wind load, both from traveling at highway speeds and cross winds from passing trucks and storms. It would be nice to have access to wind tunnel testing but for now we can estimate the effects.

PV panels drop in efficiency as they heat up, therefore they should be mounted with an air space underneath that provides adequate ventilation. This means that a panel on the trailers roof is going to act like an airfoil. Lifting forces (both up and down) will be minimized by having the same amount of air traveling on both sides of the panel (or more precisely, the same pressure). I would expect on a flat roof, a panel which is mounted equidistant from the roof (say an inch or so off the roof) would have very little in the way of airfoil effect.  However, on the curved surfaces of the Scamp, things are a little different and this is also different than mounting an awning or other item that has little frontal area.  My concern is that there will be a concentrated flow of air that follows the curve of the roof and goes under the panel, creating a good deal of lifting force at higher speeds.  This force will be variable with speed so there will be frequent pulling and pushing on the mounting surfaces. Wind from weather only adds to the effects. I don’t know how the thin fiberglass roof will hold up to these repeated stresses.

Unless there is some part of the roof in the right place that is stronger than the rest, I think the best option is to use the flat area near the roof’s edges.  On the interior, the rat fur trim is basically along the edge of this raised portion. It appears that the trim could be removed, and then some of the rat fur and insulation pulled away from the roof under the side flat portions of the roof in order to install fairly large (and hidden) backing plates. In fact, when I get into it, I might even try to install a continuous piece of sheet metal that is a little longer than the mounting brackets. Flat head bolts facing up from the interior (through the backing plates) would then be well hidden when the rat fur and insulation were re-glued.  This should provide as strong a mount as is possible, and I don’t see any advantage to adding VHB tape, 5200 or anything else because the thing that will fail first is the fiberglass body itself or the attachment to the panel (and that might take a tornado). This idea will likely require custom made mounts that follow the rise in the center roof from the front toward the rear in order to have the required space for ventilation. It is about three inches higher near the AC unit. 

Another idea is to mount the panel so it actually lies flat on the front leading edge while also raising the rear to about one to two inches over the roof (a total rise of 4-5 inches over the entire width).  This would in effect create a shallow-angle wind deflector which, at highway speeds, results in a downward and backward force but almost no lifting force. Since the panel is wider than the AC unit I expect the total air drag would still be increased.  While parked, the ventilation at the edge might be reduced but it should be good for most of the panel. You would want to park the trailer facing the sun.

Maybe something like this would work:

http://www.windynation.com/Mounting-Hardware/Windy-Nation/Adjustable-Solar-Panel-Mount-Mounting-Rack-Bracket-Boat-RV-Roof-Off-Grid/-/932?p=YzE9NDk=

This mount is intended to be put in the lowered position while underway but I wonder if it would work OK with one side raised a few inches as I just described. The one in the link would require simple modification and perhaps a third support arm would be a good idea.

Wiring is easier.  I foresee running the wires from the panel through my roof mounted fridge vent, then (in conduit) along one of two routes to the controller and battery. (If you don't have a roof fridge vent then I would bite the bullet and drill a hole for a passthrough.) The first idea is straight down and over to the sink cabinet area, then down and through the floor, under the trailer to the front sofa area. The second idea is, from the roof fridge vent, to the top of the screen door and then along the front screen door frame down into the sofa storage area.  The latter route would involve exposed conduit but it is a shorter route so the voltage loss would be a little less.

Regarding this project in general, my initial thought was to do a roof install and supplement that with a portable panel when, and if, needed.  This was for a few different reasons including the fact that I might not be good about deploying a portable panel often enough; I like the idea of charging the battery while driving (without using the tug’s alternator); portable panels are easier to steal; and the tax credit that expires the end of this year (and I am guessing would not be available for a portable unit). But with the unknowns involved and the fact that my trailer is still under warranty until September, I am considering forgoing the roof install for now and starting with a portable panel.  Then perhaps I could add the roof panel in the fall and get it all done in time to claim the tax deduction for the entire setup.

As for the Jack Antenna, I am out of room on the roof if I add a solar panel.  I plan on a TV antenna on a mast using the rear hitch, set up only when I have set up camp and bored. If you have a hitch on the back that is one option.  With the Jack Antenna, you could rotate the entire mast by sticking your arm out the back window, but since TV is for rainy days, who wants to do that. My antenna is omnidirectional.  If I can't get an interesting station, I still have a terabyte of videos to fall back on.