No, you don’t, although it can be tricky. Anyone can — in theory — buy a van and tax and insure it as a private vehicle. You will have to inform your local motor tax office that you’re changing the vehicle’s status to private use, and then you’ll be paying motor tax based on the size of the engine, so it’s best not to get anything with an engine bigger than 2.0 litres.
However, we have heard of people running up against problems with insurance when trying to do this — it seems Irish insurers (helpful as ever…) aren’t keen on vans being used for private use. A bit of shopping around, or finding a good broker, might sort that out, but it’s worth bearing in mind.
The best solution, being as you mention camping, would actually be to buy a campervan. It doesn’t have to be a full-on, hyper-expensive Volkswagen California or anything — any van that’s been converted to a camper will be much easier to insure, as they count as private vehicles anyway, and as a bonus, motor tax is only €102 per year.
Have read of our Buying a van for private use feature, too