I have a pair of the soft side crates with the mesh door and windows. I bought them for the RV, figuring they would easily fold up and be out of the way and less weight. The first time we used them, it was spring and cool. We left early in the morning and stopped along the way for breakfast. It was cool enough outside that we did not have the a/c running. We were only in the restaurant about 25 minutes. The inside of those soft crates were like a sauna. I never used them again -- worried about the dogs overheating in them. If they got that warm when it was really cool outside, I wouldn't ever use them in the summer or mid-day heat.
I went back to the open wire crates - plenty of ventilation in those.