As an ex tramper I would improve “facilities” , basic things like toilet and shower , you would only need another 3 foot of cab length to vastly improve our wellbeing. As said by others the passenger seat is nearly always surplus to requirements to , so that space could be more kitchen orientated as well. The job was bad enough 10 yrs ago but we are now lepers in most places, not wanted with nowhere to stop , yet customer still need the stuff we move.