I have no idea how long I will keep it the Promaster. One month, one year, one decade, I just don't know. If one morning I decide I'm done with van travel I want to drive to CarMax and easily sell the van in a couple of hours. You can't do this if you make permanent modifications to the van. Of course you can remove everything but that is not something you can do in a couple of hours.
Hierachy of needs