My militant girlfriend has not thus far permitted me to drill holes into the flat to install a hangboard, so I found a solution in a portable side door mounted hangboard for my van. It's all wood, collapsible, fits in the back of the van and has a pull up bar, too. I found no ideas online for smaller vans, so if anyone else has a similar predicament - check this out. Happy to share details for those who want to build their own.
Nb: it does necessitate having a roof rack, but I suppose there are workarounds if you don't.
https://www.instagram.com/sharpendclimbinguk/