Heat's not good for the guitar, I put mine out in the sun for a little while the other day it it was almost too hot to touch. Nothing happened to it but I would guess ptolonged periods like that may damage the wood or glue.
Has anyone ever done this in a climate like California? Although, N. Umbria is similar I suppose. It was when I was there during July. But it's 97F degrees here. I'm just worried about real damage.