Riverview at Pontadawe would be my recomendation, just about a quarter mile off the end of the motorway and a superb site.
Of course, there is always Gateway at Bynea or Riverside at Morriston neither I would particularly recomend but they are both very close to home for you.
Use the "Anywhere on the map" facility on the "Campsites search"............Mick
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets