Do you pilot a camper van at home, with some experience under your belt? That would help. And by “van,” does that mean something substantially smaller (noticeably narrower and presumably shorter) than a motor home, even though even motor homes in Europe are smaller than the usual versions in the U.S.?
We haven’t personally rented a camper van, but I have an observance from past Ireland trips. Roads are often much narrower there, especially on parts of the Ring of Kerry, than U.S. roads. Superhighways have wide lanes, but even those often seem narrower, and with less shoulder, than U.S. Interstates.
This wouldn’t be you, if you’re renting an Irish vehicle, but you might still need to deal with some of these: we’ve been on roads with several motorhomes, and they’re obviously having trouble staying in their lane, and are driving over the center line! Most if them had foreign license plates, particularly from Belgium or Italy, so were driving on the side the road they weren’t used to at home, with the steering wheel on the opposite side. Not that this would be you at all, but when I hear “camper” and “Ireland,” that’s what I think of.