Before I start this response, let me state that I do not own an XP Camper, I have no financial relationship with XP Camper, and I'm not posting this on behalf of anyone other than myself.
That being said, I have looked in great detail at almost every camper mentioned in this thread, and imho the XP Camper is by far the highest quality, most capable camper for 2 people to take an extended overland expedition. ...but that's irrelevant.
The reason it is irrelevant ifs that ever overland traveler ultimately has a long checklist of criteria that defines their ideal vehicle. I've seen home built fuso's, million dollar unicat's, Ford Rangers with a flippac, and everything in between. With the exception of Christian's overlanding stretch limo they are all great vehicles that do the job for their travelers.
In our case, we had our own special requirements so we built the EcoRoamer. However, it was through that process that I can to know Marc back in 2006 and have followed his progress ever since.
I can honestly say, that his first few prototypes were crappy in many ways. It's what Doug Hackney refers to as the first pancake syndrome. Where the first pancake you make on a Sunday morning always comes out crappy.
Where XP Campers is different from Doug Hackney, or me, or the dozens of people on this forum who think they have a great idea for an expedition vehicle, is that Marc has had the luxury to learn from those mistakes and constantly improve upon them. I have no doubt the the ujoint/Justin V4 camper had problems, probably a lot of them. But those have almost no relation to the quality of product that I've seen Marc putting out these days. Oh and by the way, the manufacturer (Marc) bought back the camper, so is there really anything to be whining about?
At the end of the day, we are all here because we love overland camping. The industry supporting this passion is tiny. Trying to create and compete with a new product to serve this niche market is both expensive and exhausting. (I know, I've tried) SO, my hat goes off to Marc for doing what 99% of us haven't done, which is putting his personal money and time into trying to make a fantastic product and a more robust overlanding industry.
If you're in the market for a camper of any sort/size, do your research and see what works for you.
Perhaps we should now move this thread on to something more practical like "what would YOU like to see in a next iteration" rather than more pages of why XP Campers are/aren't ___________.