The Hyundai iLoad/iMax is a great buy for what you intend to use it for, as they're big, robust and roomy boxes on wheels. Not especially quiet, refined or car-like, but well suited to a camper conversion.
However, you must ensure that the example you are looking at has a full and regular service record. This is because the well-known diesel engine and turbo failures are connected with lapsed servicing. It seems oil sludge builds up, thus starving the engine and turbo of sufficient lubrication.
But here's the tricky bit. Hyundai recommended that all scheduled servicing was carried out every 15,000km, when actually 10,000km maximum was closer to the truth for vans that were driven regularly or had a hard life. Which is most of them.
So, you need to buy on condition as well as service history, to ensure you get the promised long-life out of the iLoad/iMax. If that's the case, you can expect to hit 300,000km without any major issues. Just get that oil changed regularly!