Bryn Gloch
Bryn Gloch campsite about 5 miles outside of Caernarfon was fantastic when we went there abut 5 years ago. A lovely flat site with a river at the bottom of the camping fields, and along the road (1 mile) is a pub with a micro-brewery. The food was excellent and the natives friendly.
Hope this helps - it was a few years ago but hopefully the link i put in works and you can check out their reviews.
Have a great time.