Not 100% sure on the legality of the situation. I live in Wexford and you do see vans parked up from time to time. Most spaces would be a bit short for most vans but there are some lengthways along by harbour wall and you could park there. Tragic wardens off duty by 5:30 latest and I can’t see any other official giving you any problems. It is a great location right in the heart of town. Like everywhere if it is not abused it should be a good spot going forward. If it is, well, I can assure everyone that wexford council would be as bad or worse than any others around, and stop it completely.
In April I can’t see any issue with you staying for a night or two