Morning Shaino.
I don't know if this is you first trip into Europe or the first time to the hotter regions so, hopefully I'm not trying to teach you how to suck eggs.
Echoing some of the comments above, we don't have aircon and have comfortably survived a heatwave in Brittany where the temperatures hit 42°C for over a week.
The insulation on modern caravans is very effective at keeping heat in during cold weather and out in hot weather. Closing the blinds facing the Sun and opening windows to assist air flow with a couple of desk fans keeps things comfortable.
We have a 45 litre electric coolbox for beer wine, water and for food that doesn't need to be kept in the fridge.
I have also fitted a fridge vent fan kit which helps the caravan fridge to maintain safe low temperatures.
Keep food stuffs in sealed containers as ants especially and mice can be a real nuisance. I had ants inside the caravan last year. I ended up sprinkling ant powder around the feet of the corner steadies and on the electric cable where it left the ground to stop them from climbing up there.
We were on the Ile de Re last September and we did suffer with mosquitos, especially after dark so, take a good repellant and keep the mesh screens closed on the door, windows and roof lights. Consider also anti mosquito spray and plug-in devices. Regarding mosquitos, there is a particularly nasty species called the Tiger Mosquito which has got a foothold in parts of France and they carry all sorts of nasty diseases.
European electrical wiring standards are different to the UK and some EHU have reversed polarity. I know some caravans are designed to cope with reverse polarity but mine isn't so the fridge won't work properly. So, I take a polarity tester and conversion socket with me in case the EHU polarity is reversed.
Check to see if you need a Crit Air sticker and the Spanish equivalent for your car, as many larger cities are imposing clean air rules with hefty fines for infringement.
Don't forget to take the requisite emergency equipment in your car required for the country your in. For instance, warning triangles, two in France. Hi-Viz jacket for each occupant and within easy reach, not in the boot.
Finally, You don't mention taking dogs with you. I'm not anti dog but I am anti selfish dog owner. We had the misfortune of being next to a British couple with a motorhome and three large dogs last year. The dogs would be shut up in the motorhome while the couple went out for day trips and the dogs barked incessantly. When the couple returned and the dogs were barking he bellowed at them at the top of his voice to shut up, further disturbing the peace. French campsites are usually fairly tranquil places but this couple ruined the ambience of it for many around them and attracted numerous complaints to the management over the three weeks we were there but, it made no difference. If you are taking dogs away on holiday with you, don't leave them couped up while you go out for the day, take them with you or leave them in kennels.
Enjoy your holiday. We're back to France in May and September for six weeks, can't wait.