Re: 2002 EB diesel Quigley in Fairbanks $15.5k
Well if you're building a cabinet above counter height you have to build it over the window. If your cabinet stops half way across the window, you have to find some way to finish into the window (or leave a half window hole). There might be leaks or insulation issues, you can't drill through them, people can see the back side of your workmanship...
Those are just off the top of my head. It's certainly possible (see AndrewST build) but I think generally it would be easier to finish van wall out than windows, or at least have windows that fall into whole parts of your build. Of course nothing wrong with building counter high all around either and having lots of visibility.