I went through this with my local auto upholstery guy.  He said that
if I used regular household wallpaper, it is not designed to 'give'
around multi-curved surfaces and therefore will not fit well around
posts. Household wall-paper will (might) work on flat surfaces like
the underside of the top bed.

Special auto wall-paper that is sold through auto upholstery places is
designed to 'give' so that it will wrap around posts etc., in three
dimensions.  Also, I have been told that one needs special auto
interior adhesive that will withstand the freeze, to hot summer heat,
without loosing its grip.

The auto upholstery places have books and books of various auto
wallpapers.

M2CW,   Malcolm S