Been a few times around 6-10 years ago.
It was a lot better before all the Brits turned up!
Still a great festival though.
It’s def worth booking into a hotel or apartment if you can. as others have said, the festival goes on late into the night, with headline acts not finishing until 3am or later/earlier (you know what i mean!). So that give you very little time before the sun hits you tent and it becomes unusable.
Other alternatives are:
– book into a local camp site as it will have trees to shade your tent.
– take a cheap garden marque and remove most of the legs, so that its just a couple of feet off the ground. Nice and cool.
If you’ve got the budget, I’d recommend flying to Barcelona and spending a day or two there. Then train/drive to Port Adventura (on the way to Benicassim), which is an excellent water park and theme park (worth a day in each and there is a hotel on site).
Have fun