Step one is to download the [url=http://www.beoir.org/index.php?option=com_content&view=article&id=195:beoirfinder-app-now-available-for-android-and-ios&catid=1:latest&Itemid=99:1y849tan]Beoir Finder App[/url:1y849tan] so you can find where decent beer is sold.
If you don't have a smart phone, the same information is available in our [url=http://www.beoir.org/index.php/craft-beer-directories:1y849tan]directory[/url:1y849tan].
A search of the directory for 'dungarvan' doesn't bring up Merry's or the Lady Belle, which are the two I would recommend, though best avoid Merry's at meal times unless you are eating as it gets very busy with diners.
Dunno about Wexford other than I think The Sky and the Ground seems to get good reviews.
I would also add South 51 on south main street in Wexford, nothing there that the rest won't have but a nice airy pub if you like that and shows all the sport. If you are down around the Hook, Roches Bar in Duncannon has a nice selection of beers too but other than Metalman not sure about draught.
If you are going to go from Wexford to Dungarvan then there's a few options in Waterford City too if you are not driving. Revolution, Oscars, Philly Grimes, The Reg all have a selection and lots of others carry the local breweries. The app is definitely the way to go if you can download it.