Welcome Al and congrats on your purchase of a NEO trailer!! You will really enjoy the quality and finish of your NEO trailer.
Re your question on insulation. I contacted an outfit in Nanaimo to inquire about spray foam. They said they could not guarantee there wouldn't be some "oilcanning" Here's a definition:
Oil canning is a moderate deformation or buckling of sheet material, particularly common with flat sheet metal surfaces. It is seen as waviness in the flat areas of the metal roof or wall material.
I decided, after spending as much as I did on our trailer, that I did not want to take a chance.
So I used the rigid pink insulation between the 1" alum. ribs. I added 3" wide 5/8" plywood strips to each rib. I then added 1/2" rigid pink insulation between the plywood, then sealed (foil tape) all the seams. I then re-attached the plywood sheets to the walls screwing them to the plywood strips - no cold metal screw heads to drip moisture! See my build pictures in the link below.
Between the Maxxair fan, the factory vents, and our three windows, we have had no problems with moisture. I really like the Maxxair fan - unlike the Fantastic fan, the Maxxair has a built-in rain guard - nothing else is needed to keep the rain out.
Oh, and by the way, I did not feel the need for a vapour barrier.
Good luck with your planning and your build.
Hope this helps!