3M Crystaline Window film vs Double Pane Windows

Insulation is insulation doesn't matter if it's hot or cold.

Where are you planning to camp? For most purposes, single pane will do fine. Get the 2nd air/con if you are concerned. That will do better than an under powered single air/con. The sound from the air/con will typically drown out most noise unless it's really loud.

In the winter, dual pane does help with condensation on the inside of windows but that's not an issue in the heat.