It’s important to start with a good base. Firstly, take everything out of your van that you don’t need. You might be done in two seconds or it can be pretty time consuming. This all depends on which van you buy. With a new van you start with a clean slate, however with a second hand and older van you might have to do some work. For example, some vans will already have a specially made floor or walls in. This can be useful if you want t reuse it but stressful in you are not because it can take up some time to get it removed.
After removing everything, it is time to start creating a good base for your van so it can live on for the next few years to come. Try to remove all the rust and use some ‘water protection oil’ or ‘rust spray’ to keep your van protected. Fill in all the (screw) holes that you might have and sand them afterwards. Lastly, clean all the surfaces.