Step 1: Install the first layer which is the mineral wool on the walls and the ceiling.
What you’re gonna do is to cut the large pieces of wool into smaller ones which fit the van wall.
You need to use tapes to position pieces of wool properly.
Now place pieces of wool on the ceiling . You need to use rubber strings to keep them from falling down.
Step 2: Make 2 wooden frames for the windows on the side door and the one on the wall.
Glue them on the edges of windows and surround them with pieces of wool
You need to use some wooden bar to lean on those frames. This helps them to stay on the right position before the glue is set.
Step 3: Install aluminum foam (reflective layer)
The next layer would be aluminum foam.
Step 4: Install pallet woods as the third layer . Screw them to the walls and the ceiling.
For the walls you can use regular pallet woods but for the ceiling you should use the ones which are designed to fit together at the edges.
They are actually much thinner than pallet woods.
Make proper measurements and cuts so that the third layer of pallet woods fit well with the window frame.
Remember to drill holes to pull cables out.
