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Some, but not all, Beaufighter observer's station floors were covered with a thin sheet of plywood.  Sheets were fit to two sections of the floor, the forward-most section and aft-most section.  Plywood was not fit to the two triangular sections over the cannons.  See the drawing and the photo of a model made by Pete Fleischmann in the carousel to learn which two floor sections were covered with plywood.
 
Aircraft interior wood grain decals are available from Uschi van der Rosten (click here) and from other sources.
 
To help you cut wood grain decals to fit your Model Monkey Beaufighter radar operator/observer station's floor, here is a 2D drawing of the Model Monkey mid-war Beaufighter radar operator's station floor that can be used as a template.  Add to cart and order as if this were a model.  You will be able to download the drawing as a *.jpg file after ordering.
 
Note: depending on your printer's settings and other factors, your printer may not print this drawing at the correct scale.  When printed at the correct scale, the floor should be 134 mm long.  If necessary, adjust your printer's size setting so that the printed drawing is 134 mm to match the size of your model.