The step after planning is realization, so I went to the local home improvement store and bought some sawing rough wood at 3,69 € per meter. I additionally required several M10 screws at 90mm length for assembling the wood construction directly to the ground floor of the VW T4.
Thanks to my going-to-be-brother-in-law for all the help during the wood construction progress! I am totally surprised by the high level of functionality and very low cost for the interior simply by combining the given circumstances.
I have already spent two nights inside and do not miss any functionality of the bed and couch at all, it’s way better than I could imagine 🙂