Travel to Ireland

At that time of night I would  stay within the port area - there will be pay and display parking by the terminal buildings.

My immediate thought is to get an earlier ferry if possible. I would search out a site or two and ring to ask if you can be admitted at that time and check with the port to see if you can overnight on the dock.

Unfortunately, you’ve posted in Wildlife, Nature & the Great Outdoors but, hopefully, a mod will move the thread for you to the appropriate section where you’re more likely to get replies.

I would check with the ferry company, I can't recall if there is a lot of parking space at Dunlaoghaire but I think there are some places nearby that allow overnight motorhome parking. Or alternatively look up overnight parking on line near the harbour etc.

I have just had a look at the searchforsites website and it is showing overnight parking is permitted at West Quay Car Park.

It is several years since ferries went to Dun Laoghaire - they now use the main Dublin port area .

Yes you're right Euror, my mistake and we have docked at both. As JimE pointed out there are over night stops available. So for Dublin port itself there is one nearby on the coast, motorhomes only so ok for OP.