I decided to carpet the floor and walls of my van.  The floor was quite easy.  The walls and doors are another matter. Firstly i removed the existing ply panels inside and used a piant on sound insulation on the side panels.  Then I glued carpet underlay to the backs of the ply panels and reiftted then to improve insulation.   I used a foam backed carpet from a store sale and impact adhesive.  This is not a good idea as the carpet begins to peel off the foam backing.  At a local van converter while getting a side door window fitted, he showd me a felt type fbric he used, which stretches so can be fitted round whell arches etc.  If i do this again I would not use carpet.