Been there a few times, the house itself is pretty much environmentally sealed it's so secure
You can get to it via the old boatyard. You can get over the wall behind the train station(it's on the shore, amongst the trees, plenty of footholes), proceed through the boatyard (which is very interesting in itself, btw), and then head in the general direction of the oil terminal, and Dunglass house.
Once you get into the Oil terminal, keep your head down or the wee man will see you.
David