When you cast an AOE elemental effect spell, does is act as a grenade, emanating from one spot so that if something is behind a barrier from the spot of emanation the spell has to overcome the barrier before effecting anything behind the spell. Or does the aoe elemental effect spell fill the entire area with the elemental effect and therefore can say effect someone inside a vehicle without blasting through the vehicles windows, armor whatever.

Easiest way to think of all indirect AOE spells (such as AOE Elemental blasts) is as a grenade. Blast starts at a point, and expands to fill the area, having to deal with any barriers along the way. Obviously, this can create a "Blast in confined spaces" scenario if you're (not) careful.

I'll throw my hat in and say that I run it like a grenade explosion, but I don't believe RAW specifies either way. So, up for interpretation.