I have some experience with XPCamper and can add a few insights to the discussion. As conditions change and more owners come on-line there will be more current info, of course.
We placed one of the early V2 orders in 2013 with a due date of year's end. Later we used the prototype V2 for 3 weeks. We visited the factory in California 3 times and had many conversations with Marc, the owner. He has a very cool design that solves some limitations of other truck campers. Nothing else quite like it.
The V2 "Compact" was designed to be much simpler to make than the V1, as well as being lighter and less expensive. However, by August 2014 XPCamper still could not deliver until (maybe) November and changed some of the design features we had talked about during the year since we had ordered. In the meantime they had added V3 and V4 variations to the menu to confuse matters. Combined with issues we learned about when using the prototype and at XPCamper's suggestion, we cancelled. That was painful.
So, my advice is to treat this like a kickstarter and be patient... very patient. They are a custom shop that builds to order and everything will take longer than you expect. Plan to wait at least a year, probably longer. Unlike EarthRoamer, EarthCruiser or Tiger which supply the truck (with a few options for the base truck when ordering), with XPCamper you supply the truck which must then be modified for their mounting and weight needs. Every truck is different which throws a variable into each project. They will have your truck for weeks or months.
Speaking of weight, the XPCamper weighs about the same as other truck campers of the same size. It is a premium design with a lot of storage and extras, so the tendency to overload is great. Plan accordingly.
Research what you want thoroughly and think of yourself as an investor rather than a customer. XPCamper has completed a relatively small number of projects and have expanded their production capabilities a couple of times. As a work in progress XPCamper is interesting to follow but can be frustrating. If successful, you will be part of a small family of XPCamper owners, and you will often field questions from curious and admiring strangers.
Best wishes to Marc and his family of owners.