Now, lest you think there isn't much weight being put on here, I stepped on a scale. This pic is pretty poor, but I did have additional weight on my shoulders when I stepped on the scale, and while standing on the insulation.
The pic shows the scale, which max's out at 330 lbs.
That's right - 358 lbs total. All being supported by a 1.5 x 6 x 30 inch piece of insulation, with thin plywood on each side. This one did bow more than the other 2, obviously, but was in no danger of breaking.
So with a little math - 6 x 30 = 180 sq inches / 144 = 1.25 sq ft. 358 lbs / 1.25 = 286.4 lbs per sq ft. The 144 is sq inches per sq ft.
Probably, if I had not seen it myself, I would have trouble believing it.
So, it looks like even with thin plywood glued to insulation, it does indeed create a relatively stable wall.
Now, this does not take into account all the stresses associated with a motor home driving down the road, but it does give some idea of how well it would take weight.
And by the way, that plywood, was only $10 a sheet.
