I'm convinced that venting siding on stress skins is just as important an issue as roof panels. Particularly over urethane panels.
For the last 15 years we have recommended strapping (firring) the wall panels before siding is installed. Since urethane panels effectively have zero permeabilty, any moisture that finds it's way thru or behind the siding needs a way out. I spoke with Amos Winter about this at the Pitts conference, and he strongly agrees.
The recently discovered problems of moisture being trapped behind synthetic stucco systems should serve as warning to all of us. Just because we can't see the problem developing, doesn't mean it's not there.
We recommend vertical strapping with roll-a-vent (or something like it) at the lower edge to keep out wasps etc. At the rake, or eave the trim is held down about 1/2" from the soffit and backed again with roll-a-vent.
I realize this system raises the question of fire paths, but I have trouble beleiving it's right to convince our customers to not spec vinyl or aluminum, and then see the life expectancy of the exterior finish they chose compromised by trapped moisture.