Trawsdir is a great site, on the Harlech road just out of Barmouth on the RHS (Mountain side). It's modern (total revamp in the last 3 years.), clean and tidy, family oriented and dog friendly. They used to have seasonal pitches but best to check current availability with them direct. They're on the web. We have used them frequently in the last 3 years and fully recommend the place. You used to be able to park your car at thier sister site on the opposite side of the busy road, Caerddaniel, for the beach, otherwise it's a bit of a jaunt by foot. High up though, so great views over the bay, or look at the mountains. My avatar piccy was taken there.
Hendre Mynach is nearer to town and on the sea side of the road. Access road is a bit scary (very steep). We've only tented on there but there always seemed to be seasonal vans on site. Can't say about availability, again, call them. It too is clean though not so uber modern, but handier for the beach than Trawsdir and it's an easy (flat) walk into town along the prom. The railway line is between the site and the sea, so the views aren't so brilliant off the caravan pitches. Your on the prom though in two minutes walk.
