Hi, This has been covered quite a bit in the past and you will likely get a whole load of differing opinions of what works best in terms of internal / external etc so I can only give you my own personal opinion - I assume you are referring to the cab window screens:
I didn't want external mainly as I would not want to potentially have to pack away wet screens. I also didn't want anything that was a faff to fit, and neither did I want to attach any additional stickers or velcro or similar. The screens also had to fit well to both insulate and to provide privacy and restrict light entering.
For me, the magnetic solutions from
Project Camper ticked all of the boxes albeit slightly on the expensive side. Since owning I can thoroughly recommend them. They take maybe a minute to fit for the windscreen, and literally a few seconds to fit or remove from the door glass. Provide plenty of coverage too and also are flat enough to store on the top bed in transit
I have no association with the above company other than being pleased with their product
Hope this helps
Steve