I used to drive a truck to NI regularly a few years back , not much use to you really except to say the people of NI are generally very nice, carrickfergus has a large marina now but whether you could use the facilities I have no idea, there is a aire not too distant near Ballymena which I think is mentioned on this site, Belfast is just like any other big city with good and bad parts, the difference being you are just a few miles from open countryside, I always parked on Larne docks being nearly 60 foot and there were often camping cars nearby, I never had a problem there and it appeared neither did they, its a beautiful place to visit.