Hi,
We are going to La Sirene in August also. You are in for a treat. This will be our third year going there. The drive from Girona is really simple, basically you take the motorway just outside the airport & keep going until you cross the border, then you take the first exit on the French side & its a straight run from there. If you really don't want to drive you can get a train to Argeles but I dont know any of the times. I would recommend hetting a car as there is so much to be seen around the area that you will miss out on. However, the campsite run regular excursions to Barcelona & Andorra if you are interested. I hope you have a great holiday & best of luck with the driving - go on you can do it.

We went to St Cyprien Plage which is just along the road from Argeles last year (someone lent us a house) and the drive is very straight forward. We flew into Barcelona which is a bit further down the road but it's a straight road and Girona Airport is right beside the motorway. The area has so much to explore that you'll want a car while you're there.
I should add that we drove up from Barcelona at rush hour and drove back on the Saturday when most of Europe went on holiday and even at those times the motorway wasn't busy. We drive in Europe every year and find the driving there much less stressful and difficult than in this country. This year we are driving from Zeebrugge to Brittany rather than drive from Glasgow to the south coast and paying an extra £400 to do it.