I'm currently in the process of designing dog creates for our new van. We have 3 large Siberian Huskies to transport, most of the stuff we do is based around them, so adequate camping conditions for them is the priority.
We are converting to a camper, but going the DIY route and doing it slow as we aren't too sure yet what we actually want or need.
I'll happily provide some images once complete in the next week or so, but the leading idea so far is to have three crates the width of the van. Approx 650mm high and 1000mm deep, with the crates starting around 200mm in to the sliding door area and going back around 1/3 way down the wheel arches (LWB). This positioning specifically maximises the room available to them (with the largest dog in centre crate with no wheel arch taking up space), and most importantly, keeps the dogs away from the rear of the van, and out of the immediate crash-impact zone. The space behind will be used as a garage area for carrying mountain bikes etc.
Once installed, I'll be figuring out a way to create an exapanding bed over the crates, using them as the support base. Eventually we're planning a pop-top conversion, but as I say, this is a step at a time project.